AVS2010 Session SS-TuP: Surface Science Poster Session

In initial studies on a Ni(110) single crystal, a temperature window between approximately 350 and 450 K was identified for the ALD of the Cu acetamidinate on Ni surface: lower temperatures are insufficient for activation of the dissociative adsorption, and higher temperatures lead to continuous decomposition beyond Cu monolayer saturation. Approximately three dosing cycles are required to reach full Cu monolayer saturation, the equivalent of a film growth rate of ~0.75 Å/cycle in ALD. Preadsorption of hydrogen on the surface does not modify any of this behavior because of its rapid desorption at temperatures below 350 K once the gas-phase H₂ is removed.

The surface chemistry of the Cu precursor is complex, leading to the desorption of not only hydrogen but also butene and N-sec-butylacetamidine (H₂N-C(CH₃)=N-CH(CH₃)(CH₂CH₃)), it seems that the amidine ligands decompose via beta-hydride elimination from one of their terminal sec-butyl moieties. Copper precursors leading to relatively stable organic surface intermediates are required in ALD because their clean removal can only happen in the second half-cycle of processes that rely on hydrogenation reactions. The ligand of the copper acetamidinate precursors further decomposed on Ni (110) surfaces. The free hydrogenated amidine ligand is less reactive and no N-sec-butylacetamidine is produced by its thermal activation, but the remaining chemistry is seen with similar temperature transitions.

We studied Ag island growth on reconstructed Ge(110) and Ge(111) surfaces with low energy electron microscopy (LEEM). At 480 C, one-dimensional (1D) island growth was observed on Ge(110). Island nucleation proceeds from defects in the Ge substrate, with island thickness corresponding to the size of the substrate defect where the island nucleation occurred. As Ag is deposited, islands lengthen but do not thicken. At 9 ML, Ag coverage islands were up to 10 µm long, and thicknesses varied from 100 nm to 250 nm. One-dimensional islands were also produced by Ag deposition at room temperature followed by sample heating. Round Ag islands resolvable in LEEM were observed and coalesced into many long 1D islands as temperature was increased. Islands formed by deposition at room temperature followed by heating to a particular temperature were shorter and thicker than islands grown by deposition on a substrate held at that same temperature. Ag growth on Ge(111) is Stranski-Krastanov. Multilayer Ag island formation begins after the Ag (√3x√3)R30° phase completes at one monolayer. Ag islands exhibit hexagonal faceting. For both the Ge(111) and Ge(110) surfaces, Ag islands induce changes in the Ge substrate that leave a “footprint” observable in LEEM after all Ag has been desorbed from the surface.

*Funding from NSF CHE-0719504; NSF PHY-0649297 (REU)

The reaction of NO and CO has been studied over various transition- and noble-metal catalysts because of its importance for three-way catalytic converters. Recently, Ir-based catalysts were found to be effective for the selective reduction of NO with CO in the presence of O₂. However, the reaction mechanism, kinetics, and adsorption behavior for the NO + CO reaction on Ir-based catalyst surfaces are not fully understood.

In this study, we investigated the adsorption and thermal reactivity of NO and CO over Ir single crystals to clarify the influence of the Ir surface structure. Furthermore, we examined the kinetics and mechanism of the NO + CO reaction over Ir single crystals at high-pressure and compared the results with results for a conventional Ir/SiO₂ powder catalyst.

The kinetics of the NO reduction with CO over the Ir single crystal and the powder Ir/SiO₂ catalyst were investigated under real reaction conditions. N₂ and CO₂ were formed by the reaction of NO + CO. The Ir(111) plane showed low activity for N₂ and CO₂ production compared with the Ir(100) and Ir(211) planes. The TOFs for N₂ and CO₂ formation for the Ir planes decreased in the order (100) > (211) >> (111). The apparent activation energies for N₂ and CO₂ formation were estimated to be 107–115 kJ/mol and 110–120 kJ/mol, respectively; and these values were almost the same, regardless of the changes of the Ir surface structure. Furthermore, the order of the pre-exponential factors for the various surface structures was in good agreement with the order of the planes with respect to NO dissociation activity, indicating that the catalytic activity for NO reduction over Ir surfaces was strongly dependent on the NO dissociation activity.

The activation energies for N₂ and CO₂ formation over an Ir/SiO₂ catalyst were estimated to be 117.2 kJ/mol and 123.1 kJ/mol, respectively, and these values were similar to those of the Ir single crystal. The TOFs for N₂ and CO₂ formation over Ir/SiO₂ were almost same for those for Ir(211), which indicates that the Ir surface structure of Ir/SiO₂ was close to that of Ir(211). That is, the Ir(211) surface can be regarded as an appropriate model catalyst for the NO + CO reaction over an Ir/SiO₂ catalyst because the apparent activation energies and the TOFs for N₂ and CO₂ formation over Ir(211) were in good agreement with those over the Ir/SiO₂ catalyst.

Hydrogen termination on silicon surfaces is very important in science and technology. Hydrogen (H) is used for surface passivation, and may play role of surfactant for epitaxial growth and also present in many technological processes including chemical vapor deposition. The behavior of H on Si(100) and Si(111) surfaces is extensively studied. However, the information on interaction of H with Si(110) is very limited. The (1x1) bulk-terminated structure was reported for chemically hydrogenated Si(110) in solution [1,2]. The surface structure and processes occur on Si(110) hydrogenated in ultra-high vacuum (UHV) may be very different from chemically treated samples. There are very few reports on in situ hydrogenation of Si(110) surface. Here, we report scanning tunneling microscopy (STM) study of atomic H adsorption on Si(110) in UHV.

The high efficiency hot capillary source was used to produce atomic H flux. The large concentration of highly reactive H atoms in the flux allows us to reach surface saturation for hydrogenation at ~2 L exposure. Chemically etched tungsten tips have been used for STM (Omiron VT-system).

The initial adsorption process of hydrogen reveals itself as suppression of individual protrusions of pentagon pairs on STM image. The number of these “missing” protrusions increases with H coverage, although the overall “16x2” structure of clean Si(110) preserves. More drastic changes were observed on unreconstructed areas exposed to small amount of H at elevated temperatures. Si pentagon pairs, usually randomly distributed on these areas, were arranged in patches with local “5x4” periodicity. Further exposure at room temperature (RT) led to loosing of atomic resolution on STM images. At higher temperatures (400~500ºC) the surface have reconstructed to the zigzag row structures. Depending on relative shift of neighboring zigzag rows the local periodicity was either (2x3) or (2,1)x(0,3). The up-and-down terrace structure of “16x2” reconstruction could still be observed, probably, due to insufficient temperature to initiate massive Si transport to smooth out the surface. At temperatures more than ~550ºC the H atoms start to desorb from Si(110). These kinds of structure have not been observed before for H/Si(110) surface. No (1x1) reconstruction reported for chemically hydrogenated Si(110) was confirmed. Only small patches of (1x1) were observed in very narrow temperature window at ~350ºC.

References

[1] K. Arima, J. Ktoh, and K. Endo, Appl. Phys. Lett. 85 (2004) 6254.

[2] S. Horie, K. Arima, K. Hirose, J. Katoh, T. Ono, and K. Endo, Phis. Rev. B 72 (2005) 113306.

Mesoporous materials are widely used in industrial fields such as biotechnology and chemical engineering; catching and filtering a specific molecule, supplying novel reaction field for nanocatalysis. In particular, mesoporous silica is defined as a material with size-regulated mesopores (2-50 nm). Generally, highly-ordered arrangement of pores is attractive for chemists because the most of properties are controlled by the arrangement.

Recently some researchers reported that the internal water trapped by mesopores extraordinary behaved compared with bulk water. For examples, the water showed the lower melting point and increasing effect of non-freezing water. These phenomena were originated from the increasing ratio of interactions to water molecules from surface.

In this research, we aimed to reveal water behaviors in mesoporous silica from IR spectroscopy, Raman spectroscopy, and DSC. Mesoporous silica was synthesized conventional thermal calcinations with several organic templates because it control the pore diameters. The synthesized mesoporous silica was characterized by XRD, TEM and N2 adsorption-desorption isotherm curve.

The complete removal of organic template and the OH-termination in inside wall resulted in the presence of water in the mesopores. As the water features, we observed the both types of non-freezing and freezing water. Finally, the types of water were separated in the properties by both spectroscopy and DSC.

Low dielectric constant materials (low-k) are used as interlevel dielectrics in integrated circuits. As components have scaled and transistors have gotten closer and closer together, the insulating dielectrics have thinned to the point where charge builds up and crosstalk adversely affects the performance of the device. It is this reduction in scale which drives the need for insulating materials with lower dielectric constant. A ‘low-k’ material is one with a small value for dielectric constant relative to silicon dioxide (SiO₂) a former dielectric of choice. There are many materials with lower dielectric constants, but few of them can be suitably integrated into a semiconductor manufacturing process.

The SiO₂ is frequently used in a plasma chamber as a wafer for etching. The interaction of the plasma and the SiO₂ surface leads to incorporations/removing material for structure of SiO₂ and also to increasing of the dielectric constant. So the optimization problem in materials development for semiconductors is to lower the permittivity of the dielectric material as far as possible without compromising mechanical integrity.

The dielectric function spectra of low dielectric constant (low-k) materials have been determined using spectroscopic ellipsometry, near-normal incidence spectroscopic reflectometry, and Fourier transform infrared transmission spectrometry over a wide spectral range from 0.03 to 5.4 eV (230nm to 40.5μm wavelength region). The electronic and ionic contributions to the overall static dielectric constant were determined for representative materials used in the semiconductor industry for interlayer dielectrics. The main contributions to the static dielectric constant of the low-k materials studied were found to be the electronic and ionic absorptions.

To perform the study, square shape wafers (15x15mm) are placed in the discharge tube. The angle between wafers plane and a constructed channel is 45⁰. The DC discharge is produced in a Pyrex tube of 5mm inner diameter and an effective plasma length of 72mm. The discharge tube is evacuated using a vacuum pump that gives a base pressure of 2Pa. The working pressures from 50 to 266 Pa are achieved using a gate valve positioned above the rotary pump. Gas flow into the chamber is controlled via mass flow controllers that precisely determine gas content in the discharge tube. The working gas is a sulphur-hexafluoride (SF₆) with flow rate up to 40 sccm. The power supply used was a Keithley Model 248 high voltage supply with a maximum voltage of 5kV and discharge current of 5 mA. In this experimental campaign the maximum voltage is 2.2kV. The wafer processing time is 30 min.

It is well-known that conversion of Si(111)-(7x7) into the (√3x√3)R30^o phase of adsorbed Ag requires a change in the Si density, and causes formation of islands and holes at the surface. By mass balance, the ratio of areas of islands and holes (R_IH) should be approximately 1. However, we find that the ratio is significantly higher, depending on preparation conditions. A possible explanation would be that there are different types of (√3x√3)R30^o structures. However, neither scanning tunneling microscopy nor density functional theory (implemented as a genetic algorithm search) supports this explanation. The reason for the unexpectedly high values of R_IH is unknown.

P.A.C.S. Numbers 68.37.Ef, 68.55.-a, 81.15.Aa, 68.47

Silver electroplating is commonly used to provide low electrical loss characteristics for RF and microwave devices. These RF devices can also be susceptible to multipactor discharge, a resonant electron phenomenon that relies on electron density growth by secondary electron emission. The secondary electron yield (SEY) can determine whether a multipactor discharge can form; therefore, understanding SEY variations in silver surfaces is necessary for accurate multipactor breakdown prediction. In this work, SEY is measured for a variety of silver surfaces using a retarding potential method. Starting with as-received silver with no specific surface preparation, SEY values are shown to be considerably increased due to adsorbed gases on both bulk and electrodeposited silver substrates. Auger analysis was performed to determine the contaminant layers, as it is these technical silver surfaces that are realistic for space hardware where in-situ surface conditioning is not possible. Additional SEY measurements were performed on both polycrystalline and single crystal silver surfaces to determine the effect of the crystalline orientation on the SEY. Different crystallographic orientations at the surface of the electrodeposit may arise due to differences in plating variables such as bath chemistry, electrode geometry and localized current density. These measurements serve to better understand possible improvements in plating processes to minimize secondary electron emission and multipactor risk. Lastly, the effect of baking and multipactor conditioning on silver SEY is presented. Formation of thin carbon films are observed as a result of multipactor exposure, and x-ray photoelectron and Raman spectroscopy film analysis results are presented.

The activity of methanol on Ni-Au and Pt-Au clusters deposited at 300 K on TiO₂ (110) was investigated using temperature programmed desorption (TPD), scanning tunneling microscopy (STM), and low energy ion scattering (LEIS). Bimetallic clusters were grown by first depositing the metal with stronger metal-support interactions (Ni or Pt) onto the surface in order to seed the more mobile Au at existing Ni or Pt clusters. The preexisting Ni or Pt clusters also inhibited the sintering of Au at higher temperatures. The composition at the surface of the clusters was established by the major products observed in TPD experiments. Methyl (~717 K) was produced on the TiO₂ support, CO (~429 and ~775 K) and H₂ (~357 K) were produced at Ni sites, and formaldehyde (~580 K) production was attributed to the Au-titania interface. CO (~503 K) and H₂ (~503 K) were also characteristic of Pt at the surface. LEIS data for 0.25 ML of total coverage shows that for clusters with > 50% bulk Au composition, the surface of the cluster is almost entirely pure Au. TPD of methanol on clusters with > 50% bulk Au composition still show activity characteristic of Ni or Pt at the surface, suggesting that methanol is able to induce the migration of Ni and Pt to the surface of the clusters. Increasing the amount of Au on the surface for pure Au clusters beyond 1 ML resulted in a decrease of the formaldehyde signal, which is attributed to a subsequent decrease in the Au-TiO₂ interface as more Au is deposited onto the surface. Formaldehyde production on 0.25 ML of pure Au and 25% Ni / 75% Au clusters showed no decrease in activity even after 6 consecutive TPD cycles to 800 K.

As the sizes of the devices are quickly approaching the nanometer scale in the microelectronics industry, the need to control reactions at the molecular level and at the interface becomes very important for developing cleaner deposition techniques. For example, metal contacts grown using atomic layer deposition (ALD) have already made an impact on modern devices.

A common precursor used to grown copper metal contact, Cu^I (hexafluoroacetylacetonato) vinyltrimethylsilane or Cu(hfac)VTMS, has been previously studied at the molecular level on Si(100)-2x1 and other surfaces using surface sensitive techniques. Here we use this precursor as a reactant on several functionalized silicon surfaces to produce and control the size distribution of metallic nanoparticles.

We compare the reaction of Cu(hfac)VTMS with H-Si, NH₂-Si, NH-Si, and OH-Si surface reactive sites and follow it by in situ infrared spectroscopy (FTIR), temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and complement with Density Functional Theory calculations. The growth of the hfac vibrational signatures indicates reaction on these functionalized surfaces and losses in the Si-H stretch spectral region can be used to follow the deposition kinetics. The surface is used here as a reducing agent providing the hydrogen to remove the ligands of the copper deposition precursor and to produce metallic nanostructures.

Soft- and reactive landing of mass-selected ions onto surfaces is a unique approach for the highly controlled preparation of catalyst materials that are often inaccessible using conventional synthesis techniques. Mass selection allows polyatomic ions with known charge and chemical identity to be deposited onto surfaces under carefully controlled conditions, thereby avoiding purification steps which are typically necessary with traditional catalyst preparation methods. A new apparatus has been designed and assembled at PNNL that allows in situ reactivity and time of flight secondary ion mass spectrometry analysis of surfaces prepared or modified through soft- and reactive landing. The capabilities of this instrument for the preparation and analysis of catalyst materials are demonstrated for two different systems consisting of monolayer catalysts produced by the deposition of organometallic metal-salen and ruthenium bipyridine cations onto self assembled monolayer surfaces. It is shown that through soft landing of vanadium-salen cations and a proton donor it is possible to achieve proton mediated reactivity in an inert fluorinated monolayer that is normally only observed in highly acidic solutions. In addition, it is demonstrated that gas-phase ligand stripping may be used to generate highly reactive undercoordinated metal complexes which exhibit enhanced activity towards reactive landing in comparison to fully ligated species. The immobilized complexes, which are covalently bound to the surface, are shown to exhibit catalytic activity when exposed to gaseous reagents.

The satellites in X-Ray photoemission spectroscopy, XPS, can provide information about the electronic structure, especially for ionic materials. [1,2] We present a new analysis of the XPS satellites that, when applied to CeO₂ which is an important substrate for model studies of catalysis, enables a new understanding of this material. While the origin of intra-atomic effects in terms of atomic near-degeneracies is well understood, [1] there are two different ways of describing the inter-atomic effects that lead to satellites. The first is to ascribe the satellites to charge transfer, CT, from ligands, or other neighboring atoms, into unoccupied or partly occupied shells of the ionized atom. This interpretation is commonly applied to oxides and other ionic crystals. [2] In the CT model, the satellites gain intensity through the mixing of XPS allowed configurations with XPS forbidden configurations. However, changes in the orbitals between the initial and final states are normally neglected in the CT model. On the other hand, the second way of understanding satellites as shake satellites, [3,4]ascribes the driving force for the loss of intensity from the main peak into the satellites to the orbital relaxation, which screens the core-hole. This orbital relaxation allows valence excited, or shake, states to obtain intensity. [3] However, both mechanisms must be taken into account to correctly describe the inter-atomic contributions to XPS satellites and, in the present work, we reconcile these two different points of view. We show that the covalent mixing of metal and ligand orbitals in the wavefunctions, for both initial and final states, is a powerful way to understand the intensities of satellites due to inter-atomic effects. For the XPS of NiO, where both intra and inter-atomic effects must be taken into account, our analysis of the CI wavefunctions shows the underlying covalent character of the main and satellite peaks. We also stress the importance of covalent mixing in the initial state in order for there to be substantial satellite intensity. We show that different degrees of covalent character in the initial states of CeO₂ and LaAlO₃ lead to very different satellite energies and intensities for the isoelectronic metal cations. Our analysis provides direct and unambiguous evidence that the inter-atomic satellite features are closely related to the covalent binding in the material.

(1) PS Bagus, ES Ilton: Phys. Rev. B 73, 155110 (2006).

(2) FMF de Groot: J. Electron Spectrosc. Relat. Phenom. 67, 529 (1994).

(3) T Aberg: Phys. Rev. 156, 35 (1967).

(4) L Sangaletti, F Parmigiani, PS Bagus: Phys. Rev. B 66, 115106 (2002).

XPS has been used to analyse the ash released from a number of volcanoes, including that from Mount St Helens, USA and Eyjafjallajökull, Iceland. The results indicate that the differences in the composition of the basalt from different regions reflect the geological structure of the region. Some of the compositional differences depend upon whether the geological plates are moving together, causing more crust material to be mixed with the lava or whether the plates are moving apart and so the lava is predominantly from sub-surface sources. Further complications arise from the fact that the ash from some eruptions (e.g. Eyjafjallajökull) also contains material from an overlaying glacier. It has been found that the material from Eyjafjallajökull is richer in calcium than that from Mt St Helens.

The use of XPS to fingerprint this type of material has been investigated. The effect of ion sputtering of the material has also been investigated as a means to generate more representative data.

Recently, the ethanol electro-oxidation reaction has attracted considerable attention because of the advantages of using ethanol as fuel in liquid fuel cells.¹ Ethanol can be produced from renewable biomass sources, and has high energy density and less toxic than methanol. However, the ethanol oxidation kinetics is slow, impeding its use in the direct ethanol fuel cells (DEFCs). Tremendous efforts have been made to develop new ethanol oxidation catalysts to improve its efficiency. Binary Pt-Sn alloy catalysts are some of the more extensively investigated anode materials for DEFCs. It was found that the increased activity of binary electrocatalysts with respect to Pt alone was attributed to the bifunctional effect and electronic interaction between Pt and alloyed metals.^2,3,4 However, studies from supported nanocatalyst show disagreements in mechanism of what degree of alloying between Pt and Sn and what amount of Sn alloyed with Pt will improve the activity of the electrocatalysts towards EOR. ^{5, 6, 7, 8} It is still unclear whether the alloyed Sn, or the SnO₂ phase is the reason in the increase in Pt-Sn electrocatalysts activity towards EOR.^{1, 5-8}

In the work presented here, we are investigating surface alloy of Pt-Sn/Pt(111) and SnO2/Pt(111) as model catalysts for ethanol electro-oxidation. Characterization is performed by a combination of surface science techniques (X-Ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), temperature programmed desorption (TPD), and low energy ion scattering spectroscopy (LEISS)) and classical electrochemical measurements. This integrated approach can be used to identify the fundamental properties of SnO₂/Pt(111) and Sn-Pt/Pt(111) electrodes and to correlate them with the activity of each electrode towards EOR.

1. E. Antolini, J. Power Sources 170 (2007) 1-12

2. Rigsby, M. A., Zhou, W. –P, Lewera, A., Duong, H. T., Bagus, P. S., Jaegermann, W., Hunger, R., and Wieckowski, A., Eperiment and Theory of Fuel Cell Catalysis: Methanol and Formic Acid Decomposition on Nanoparticle Pt/Ru. J. Phys. Chem. C, 2008 112 (39) 15595-15601

3. N. M. Markovic, H. A. Gasteiger, P. N. Ross, X. Jiang, I. Villegas, M. J. Weaver, Electrochim. Acta 40 (1995) 91

4. S. L. Goikovic, T. R. Vidakovic, D. R. Durovic, Electrochim. Acta 48 (2003) 3607

5. C. Lamy, S. Rousseau, E. M. belgsir, C. Countanceau, J.-M Leger, Electrochim. Acta 49 (2004) 3901

6. W. Zhou, Z. Zhou, S. Song, W. Li, G. Sun, P. Tsiakaras, Q. Xin, Appl. Catal. B 46 (2003) 273

7. L. Jiang, G. Sun, S. Sun, J. Liu, S. Tang, H. Li, B. Zhou, Q. Xin, Electrochim. Acta 50 (2005) 5384

8. F. Colmati, E. Antolini, E. R. Gonzalez, J. Electrochem. Soc. 154 (2007) B39

The application of XPS C₆₀ sputter depth profiling to characterize synthesized poly-glycidyl methacrylate (PGMA) brush-like thin film structures will be presented. In contrast to low voltage (250 V) Ar sputtering, C₆₀ sputtering with XPS analysis was able to obtain quantitative chemical state information as a function of depth with minimal ion beam induced chemical damage. To minimize sputtering artifacts and improve interface definition, Zalar (azimuthal) rotation and appropriate instrument geometry for C₆₀ sputter depth profiling was used for this work. The XPS depth profiles show the chemical changes associated with various solutions applied to these organic films.

Airborne particles have well-documented effects on human health, visibility, and the chemistry of the atmosphere. Particles play a major role in climate change and are a large source of uncertainty in model predictions of global warming. A significant part of this uncertainty is the lack of understanding of the nature of the organic component. This deficiency includes the chemical speciation and the distribution of the organics between the surface and the bulk of liquid particles, as well as changes due to oxidation during transport in the atmosphere.

Self-assembled monolayers (SAMs) represent a well-defined system for elucidating mechanisms of mixed gas-condensed phase reactions and serve as proxies for organic-coated airborne dust particles. Previous studies have shown that ozone reactions of terminal alkene-silane SAMs generates surface-bound acids, aldehydes, and secondary ozonide (SOZ), as well as gaseous products such as CO, CO₂, HCHO, and HCOOH. In addition, the surprising formation of large, hydrophobic organic particles was observed by AFM and Auger electron spectroscopy. A particularly noteworthy result of atmospheric interest is that the uptake of water was not increased upon oxidation of these films, despite the formation of polar carbonyl-containing groups, and SOZ. This has important implications for particles in the atmosphere, since it is generally assumed that oxidation converts hydrophobic surfaces to hydrophilic which take up water more readily, thereby affecting visibility and cloud formation.

The goal of this work was to determine the product functional groups and the 3-D structure of particles produced from the ozonolysis of SAMs formed by attachment of 7−octenyltrichlorosilane (C8= SAM) to silica substrates. A combination of analytical techniques such as single particle FTIR, NanoSIMS, and TOF-SIMS were utilized to study the surface composition and morphology after oxidation. Atmospheric implications for the 3-D structure of SOA, SAM reactions and stability in air, ozonolysis of alkenes on surfaces, and the oxidation of alkenes on airborne dust particles will be discussed.

The adsorption kinetics of CO on Cr(110) and on Cr₂O₃(0001)/Cr(110) was investigated using temperature programmed desorption (TPD). The adsorption of CO was performed with the substrate maintained at 120 K, and a feedback control system was used to generate linear heating rates. For the Cr₂O₃(0001)/Cr(110) surface a saturation coverage of CO was measured to occur at 0.5 L. The desorption kinetics is estimated to be 1^st order with an attractive lateral interaction between CO molecules. The Redhead method was used to measure the activation energy for desorption of the CO. This analysis resulted in a value of 49.2 kJ/mol ± 2.6 kJ/mol for the activation energy. For the adsorption of CO on Cr(110) no CO desorption is detected for coverage below 0.5 L. This indicates that at this coverage all of the CO is dissociating and reacting with the Cr(110) surface. Deposition of 1L CO on clean Cr(110) shows only one broad signal at 300 K. By deposition of 2 L of CO or larger, a shift of the signal to 280 K and the appearance of a second signal at 210 K can be observed. The broadening and shifting of the desorption signals can be attributed to the lateral interact between the CO molecules and their adsorption on different binding sites on the Cr(110) surface.