Thermal Desorption Of CO Research Articles

Stability of Graphene/Intercalated Oxygen/Ru(0001) as Studied by Thermal Desorption of CO and CO2 Molecules

Formation of graphene on Ru(0001) by exposure to ethylene and subsequent annealing has been studied by low-energy electron diffraction, X-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy. The stability of graphene/intercalated oxygen/Ru(0001) has been investigated by temperature programmed desorption spectroscopy. Desorption of CO and CO2 was observed upon heating the samples to temperatures above 700 K. It was found that the graphene layer was partly intact after the desorption run and that the intercalated oxygen was removed. It was concluded that the oxygen-intercalated graphene layer was stable up to temperatures of about 700 K.

Resolving desorption of complex organic molecules in a hot core

Context. The presence of many interstellar complex organic molecules (COMs) in the gas phase in the vicinity of protostars has long been associated with their formation on icy dust grain surfaces before the onset of protostellar activity, and their subsequent thermal co-desorption with water, the main constituent of the grains’ ice mantles, as the protostar heats its environment to ~100 K. Aims. Using the high angular resolution provided by the Atacama Large Millimetre/submillimetre Array (ALMA), we want to resolve the COM emission in the hot molecular core Sagittarius B2 (N1) and thereby shed light on the desorption process of COMs in hot cores. Methods. We used data taken as part of the 3 mm spectral line survey Re-exploring Molecular Complexity with ALMA (ReMoCA) to investigate the morphology of COM emission in Sagittarius B2 (N1). We also used ALMA continuum data at 1 mm taken from the literature. Spectra of ten COMs (including one isotopologue) were modelled under the assumption of local thermodynamic equilibrium (LTE) and population diagrams were derived for these COMs for positions at various distances to the south and west from the continuum peak. Based on this analysis, we produced resolved COM rotation temperature and column density profiles. H2 column density profiles were derived from dust continuum emission and C18O 1–0 emission and used to derive COM abundance profiles as a function of distance and temperature. These profiles are compared to astrochemical models. Results. Based on the morphology, a rough separation into O- and N-bearing COMs can be done. The temperature profiles span a range of 80–300 K with power-law indices from −0.4 to −0.8, which is in agreement with expectations of protostellar heating of an envelope with optically thick dust. Column density and abundance profiles reflect a similar trend as seen in the morphology. While abundances of N-bearing COMs peak only at the highest temperatures, those of most O-bearing COMs peak at lower temperatures and remain constant or decrease towards higher temperatures. Many abundance profiles show a steep increase at ~100 K. To a great extent, the observed results agree with results of astrochemical models that, besides the co-desorption with water, predict that O-bearing COMs are mainly formed on dust-grain surfaces at low temperatures, while at least some N-bearing COMs and CH3CHO are substantially formed in the gas phase at higher temperatures. Conclusions. Our observational results, in comparison with model predictions, suggest that COMs that are exclusively or, to a great extent, formed on dust grains desorb thermally at ~100 K from the grain surface, likely alongside water. A dependence on the COM binding energy is not evident from our observations. Non-zero abundance values below ~100 K suggest that another desorption process of COMs is at work at these low temperatures: either non-thermal desorption or partial thermal desorption related to the lower binding energies experienced by COMs in the outer, water-poor ice layers. In either case, this is the first time that the transition between two regimes of COM desorption has been resolved in a hot core.

Oxygen plasma etching of hydrocarbon‐like polymers: Part I Modeling

This work on the etching of polymers in oxygen plasmas begins with a general review of experimental data and modeling attempts. Result analysis leads to an extended etching model based on the description of polymer surfaces composed of chain segments randomly distributed and taking into account the microscopic structure of polymers at the atomic and molecular level. Experimental data also suggest that thermally activated desorption of CO, in addition to CO2 desorption, and UV‐induced etching, in addition to ion‐induced etching, must be incorporated in the modeling. The analytical results confirm the impossibility to reach perfect anisotropy in presence of UV‐induced desorption and also to determine directly from Arrhenius plots the activation energies for CO and CO2 thermal desorption.

Methanol ice co-desorption as a mechanism to explain cold methanol in the gas-phase

Context. Methanol is formed via surface reactions on icy dust grains. Methanol is also detected in the gas-phase at temperatures below its thermal desorption temperature and at levels higher than can be explained by pure gas-phase chemistry. The process that controls the transition from solid state to gas-phase methanol in cold environments is not understood. Aims. The goal of this work is to investigate whether thermal CO desorption provides an indirect pathway for methanol to co-desorb at low temperatures. Methods. Mixed CH3OH:CO/CH4 ices were heated under ultra-high vacuum conditions and ice contents are traced using RAIRS (reflection absorption IR spectroscopy), while desorbing species were detected mass spectrometrically. An updated gas-grain chemical network was used to test the impact of the results of these experiments. The physical model used is applicable for TW Hya, a protoplanetary disk in which cold gas-phase methanol has recently been detected. Results. Methanol release together with thermal CO desorption is found to be an ineffective process in the experiments, resulting in an upper limit of ≤ 7.3 × 10−7 CH3OH molecules per CO molecule over all ice mixtures considered. Chemical modelling based on the upper limits shows that co-desorption rates as low as 10−6 CH3OH molecules per CO molecule are high enough to release substantial amounts of methanol to the gas-phase at and around the location of the CO thermal desorption front in a protoplanetary disk. The impact of thermal co-desorption of CH3OH with CO as a grain-gas bridge mechanism is compared with that of UV induced photodesorption and chemisorption.

The Flying Saucer: Tomography of the thermal and density gas structure of an edge-on protoplanetary disk

Context. Determining the gas density and temperature structures of protoplanetary disks is a fundamental task in order to constrain planet formation theories. This is a challenging procedure and most determinations are based on model-dependent assumptions. Aims. We attempt a direct determination of the radial and vertical temperature structure of the Flying Saucer disk, thanks to its favorable inclination of 90 degrees. Methods. We present a method based on the tomographic study of an edge-on disk. Using ALMA, we observe at 0.5″ resolution the Flying Saucer in CO J = 2–1 and CS J = 5–4. This edge-on disk appears in silhouette against the CO J = 2–1 emission from background molecular clouds in ρ Oph. The combination of velocity gradients due to the Keplerian rotation of the disk and intensity variations in the CO background as a function of velocity provide a direct measure of the gas temperature as a function of radius and height above the disk mid-plane. Results. The overall thermal structure is consistent with model predictions, with a cold (<12−15 K) CO-depleted mid-plane and a warmer disk atmosphere. However, we find evidence for CO gas along the mid-plane beyond a radius of about 200 au, coincident with a change of grain properties. Such behavior is expected in the case of efficient rise of UV penetration re-heating the disk and thus allowing CO thermal desorption or favoring direct CO photo-desorption. CO is also detected at up to 3–4 scale heights, while CS is confined to around 1 scale height above the mid-plane. The limits of the method due to finite spatial and spectral resolutions are also discussed. Conclusions. This method appears to be a very promising way to determine the gas structure of planet-forming disks, provided that the molecular data have an angular resolution which is high enough, on the order of 0.3−0.1″ at the distance of the nearest star-forming regions.

DCO+, DCN, and N2D+reveal three different deuteration regimes in the disk around the Herbig Ae star HD 163296

The formation pathways of deuterated species trace different regions of protoplanetary disks and may shed light into their physical structure. We aim to constrain the radial extent of main deuterated species; we are particularly interested in spatially characterizing the high and low temperature pathways for enhancing deuteration of these species. We observed the disk surrounding the Herbig Ae star HD 163296 using ALMA in Band 6 and obtained resolved spectral imaging data of DCO$^+$ ($J$=3-2), DCN ($J$=3-2) and N$_2$D$^+$ ($J$=3-2). We model the radial emission profiles of DCO$^+$, DCN and N$_2$D$^+$, assuming their emission is optically thin, using a parametric model of their abundances and radial excitation temperature estimates. DCO$^+$ can be described by a three-region model, with constant-abundance rings centered at 70 AU, 150 AU and 260 AU. The DCN radial profile peaks at about ~60 AU and N$_2$D$^+$ is seen in a ring at ~160 AU. Simple models of both molecules using constant abundances reproduce the data. Assuming reasonable average excitation temperatures for the whole disk, their disk-averaged column densities (and deuterium fractionation ratios) are 1.6-2.6$\times 10^{12}$ cm$^{-2}$ (0.04-0.07), 2.9-5.2$\times 10^{12}$ cm$^{-2}$ ($\sim$0.02) and 1.6-2.5 $\times 10^{11}$ cm$^{-2}$ (0.34-0.45) for DCO$^+$, DCN and N$_2$D$^+$, respectively. Our simple best-fit models show a correlation between the radial location of the first two rings in DCO$^+$ and the DCN and N$_2$D$^+$ abundance distributions that can be interpreted as the high and low temperature deuteration pathways regimes. The origin of the third DCO$^+$ ring at 260 AU is unknown but may be due to a local decrease of ultraviolet opacity allowing the photodesorption of CO or due to thermal desorption of CO as a consequence of radial drift and settlement of dust grains.

Different dust and gas radial extents in protoplanetary disks: consistent models of grain growth and CO emission

ALMA observations of protoplanetary disks confirm earlier indications that there is a clear difference between the dust and gas radial extents. The origin of this difference is still debated, with both radial drift of the dust and optical depth effects suggested in the literature. In this work, the feedback of realistic dust particle distributions onto the gas chemistry and molecular emissivity is investigated, with a particular focus on CO isotopologues. The radial dust grain size distribution is determined using dust evolution models that include growth, fragmentation and radial drift. A new version of the code DALI is used to take into account how dust surface area and density influence the disk thermal structure, molecular abundances and excitation. The difference of dust and gas radial sizes is largely due to differences in the optical depth of CO lines and millimeter continuum, without the need to invoke radial drift. The effect of radial drift is primarily visible in the sharp outer edge of the continuum intensity profile. The gas outer radius probed by $^{12}$CO emission can easily differ by a factor of $\sim 2$ between the models for a turbulent $\alpha$ ranging between typical values. Grain growth and settling concur in thermally decoupling the gas and dust components, due to the low collision rate with large grains. As a result, the gas can be much colder than the dust at intermediate heights, reducing the CO excitation and emission, especially for low turbulence values. Also, due to disk mid-plane shadowing, a second CO thermal desorption (rather than photodesorption) front can occur in the warmer outer mid-plane disk. The models are compared to ALMA observations of HD 163296 as a test case. In order to reproduce the observed CO snowline of the system, a binding energy for CO typical of ice mixtures needs to be used rather than the lower pure CO value.

MULTIPLE CARBON MONOXIDE SNOW LINES IN DISKS SCULPTED BY RADIAL DRIFT

ABSTRACT Observations of protoplanetary disks suggest that the gas and dust follow significantly different radial distributions. This finding can be theoretically explained by a combination of radial drift and gas drag of intermediate-sized dust grains. Using a simple parametric model to approximate the different distributions of the gas and dust components, we calculate and examine the impact of radial drift on the global dust temperature structure. We find that the removal of large grains beyond the “truncation radius” allows this region to become significantly warmer from reprocessed stellar radiation shining down from the disk upper layers, increasing the outer disk temperature by ∼10%–30%. This change is sufficient to raise the local temperature to a value exceeding the CO desorption temperature. These findings imply that the disk density structures induced by radial drift are able to create multiple CO snow lines. The inner disk CO is in the gas phase, freezing out near the classical snow line at R ∼ 20 – 40 AU ?> . Moving outward, the CO sublimates once again beyond the truncation radius (80 AU in our models) and subsequently re-freezes out at sufficiently large stellar distances beyond R ≳ 130 – 200 AU ?> . We find that thermal desorption of CO in the outer disk becomes competitive with external UV photodesorption and that this additional transition from solid state CO to the gas phase has significant implications for the C/O ratio in the outer disk.

DOUBLE DCO+RINGS REVEAL CO ICE DESORPTION IN THE OUTER DISK AROUND IM LUP

In a protoplanetary disk, a combination of thermal and non-thermal desorption processes regulate where volatiles are liberated from icy grain mantles into the gas phase. Non-thermal desorption should result in volatile-enriched gas in disk-regions where complete freeze-out is otherwise expected. We present ALMA observations of the disk around the young star IM Lup in 1.4 mm continuum, C18O 2-1, H13CO+ 3-2 and DCO+ 3-2 emission at ~0".5 resolution. The images of these dust and gas tracers are clearly resolved. The DCO+ line exhibits a striking pair of concentric rings of emission that peak at radii of ~0".6 and 2" (~90 and 300 AU, respectively). Based on disk chemistry model comparison, the inner DCO+ ring is associated with the balance of CO freeze-out and thermal desorption due to a radial decrease in disk temperature. The outer DCO+ ring is explained by non-thermal desorption of CO ice in the low-column-density outer disk, repopulating the disk midplane with cold CO gas. The CO gas then reacts with abundant H2D+ to form the observed DCO+ outer ring. These observations demonstrate that spatially resolved DCO+ emission can be used to trace otherwise hidden cold gas reservoirs in the outmost disk regions, opening a new window onto their chemistry and kinematics.

CO desorption from a catalytic surface: elucidation of the role of steps by velocity-selected residence time measurements.

Directly measuring the rate of a surface chemical reaction remains a challenging problem. For example, even after more than 30 years of study, there is still no agreement on the kinetic parameters for one of the simplest surface reactions: desorption of CO from Pt(111). We present a new experimental technique for determining rates of surface reactions, the velocity-selected residence time method, and demonstrate it for thermal desorption of CO from Pt(111). We use UV−UV double resonance spectroscopy to record surface residence times at selected final velocities of the desorbing CO subsequent to dosing with a pulsed molecular beam. Velocity selection differentiates trapping-desorption from direct scattering and removes influences on the temporal profile arising from the velocity distribution of the desorbing CO. The kinetic data thus obtained are of such high quality that bi-exponential desorption kinetics of CO from Pt(111) can be clearly seen. We assign the faster of the two rate processes to desorption from (111) terraces, and the slower rate process to sequential diffusion from steps to terraces followed by desorption. The influence of steps, whose density may vary from crystal to crystal, accounts for the diversity of previously reported (single exponential) kinetics results. Using transition-state theory, we derive the binding energy of CO to Pt(111) terraces, D(0)(terr) (Pt−CO) = 34 ± 1 kcal/mol (1.47 ± 0.04 eV) for the low coverage limit (≤0.03 ML) where adsorbate−adsorbate interactions are negligible. This provides a useful benchmark for electronic structure theory of adsorbates on metal surfaces.

Size effect on thermal desorption of CO from Pt nanostructures on graphite

Self-assembled Pt nanostructures, which are formed by evaporation and subsequent diffusion limited aggregation of Pt on graphite, have been studied by photoemission and scanning electron microscopy. Adsorption of CO has been studied by temperature programmed desorption. Charge induced Pt 4f core level shifts in the order of 1 eV that depend on the effective dimensions of the nanostructures have been observed, and effective dimensions of the Pt structures have been defined based on the Pt 4f core level shifts. The effective dimensions of the Pt structures have been correlated with changes in the thermal desorption of adsorbed CO. It is observed that smaller effective dimensions in the few nanometer range result in lower desorption temperatures of up to 50 K. The possible role of hot electrons in the adsorption process has been discussed.

Study of oxygen groups at a porous carbon surface by a new fast intermittent thermodesorption technique

A threshold thermodesorption method, named fast Intermittent TPD (ITPD), was used to study the evolution of CO 2 and CO arising from the decomposition of oxygen groups at the surface of a porous carbon used in the wastewater treatment. Applied to the as-received carbon, CO 2-ITPD provided clear evidence for six values of the apparent activation energy of oxygen group decomposition ( E app ): 139, 168, 206, 237, 270 and 290 kJ mol −1. Corresponding apparent pre-exponential factors ( A app ) were also determined. The data ( E app and A app ) derived from ITPD for the six desorption steps allowed a successful description of the complete TPD profile, considering a Gaussian narrow distribution of E app for each step. CO-ITPD also showed the presence of six (possibly seven) distinguishable steps upon CO thermal desorption and further demonstrated the interest of the fast ITPD technique for studying carbon surface chemistry. The TPD and ITPD profiles of the carbon treated with sodium hypochlorite showed: (i) a sharp increase in the amount of desorbed species, (ii) the prevailing presence of less stable oxygen groups, mainly carboxylic acids, giving rise to CO 2 desorption at low temperature, and (iii) the progressive merging of the desorption steps detectable at low temperature upon increasing surface density of oxygen groups.

New results on thermal and photodesorption of CO ice using the novel InterStellar Astrochemistry Chamber (ISAC)

Aims. We present the novel InterStellar Astrochemistry Chamber (ISAC), designed for studying solids (ice mantles, organics, and silicates) in interstellar and circumstellar environments: characterizing their physico-chemical properties and monitoring their evolution as caused by (i) vacuum-UV irradiation; (ii) cosmic ray irradiation; and (iii) thermal processing. Experimental study of thermal and photodesorption of the CO ice reported here simulates the freeze-out and desorption of CO on grains, providing new information on these processes.Methods. ISAC is an UHV set-up, with base pressure down to P = 2.5 × 10-11 mbar, where an ice layer is deposited at 7 K and can be UV-irradiated. The evolution of the solid sample was monitored by in situ transmittance FTIR spectroscopy, while the volatile species were monitored by QMS. Results. The UHV conditions of ISAC allow experiments under extremely clean conditions. Transmittance FTIR spectroscopy coupled to QMS proved to be ideal for in situ monitoring of ice processes that include radiation and thermal annealing. Thermal desorption of CO starting at 15 K, induced by the release of H2 from the CO ice, was observed. We measured the photodesorption yield of CO ice per incident photon at 7, 8, and 15 K, respectively yielding 6.4 ± 0.5 × 10-2 , 5.4 ± 0.5 × 10-2 , and 3.5 ± 0.5 × 10-2 CO molecules photon (7.3–10.5 eV)-1 . Our value of the photodesorption yield of CO ice at 15 K is about one order of magnitude higher than the previous estimate. We confirmed that the photodesorption yield is constant during irradiation and independent of the ice thickness. Only below ~ 5 monolayers ice thickness the photodesorption rate decreases, which suggests that only the UV photons absorbed in the top 5 monolayers led to photodesorption. The measured CO photodesorption quantum yield at 7 K per absorbed photon in the top 5 monolayers is 3.4 molecules photon-1 . Conclusions. Experimental values were used as input for a simple model of a quiescent cloud interior. Photodesorption seems to explain the observations of CO in the gas phase for densities below 3–7 × 104 cm-3 . For the same density of a cloud, 3 × 104 cm-3 , thermal desorption of CO is not triggered until T = 14.5 K. This has important implications for CO ice mantle build up in dark clouds.

The character of interactions of CO, H2, and CH3OH with the surface of γ-Al2O3 and Cu-Zn oxide catalyst

The thermal desorption of CO, H2, and CH3OH from the surface of Katalco-58 industrial catalyst for the synthesis of methanol and γ-Al2O3 was studied. Weak interaction of the gases with the surface of samples was observed over the temperature range 75–400°C. The desorption of the gases obeyed the second-order Wigner-Polyani equation. The desorption energies of the gases were calculated. The mechanism of dimethyl ether synthesis was studied.

Fe-promotion of supported Rh catalysts for direct conversion of syngas to ethanol

The influences of support (silica or titania) and loading of Fe promoter on the activity and selectivity of Rh-based catalysts for the direct synthesis of ethanol from syngas were explored. The reaction was performed in a fixed-bed reactor system typically operating at 543 K, 20 atm, WHSV of 8000 cm 3 g −1 cat h −1 and H 2:CO ratio of 1:1. Characterization by H 2 chemisorption and electron microscopy indicated that rhodium was very highly dispersed on the supports and was in direct contact with the Fe promoter. Although little ethanol was produced over 2 wt% Rh on silica, a similar loading of Rh on titania was active for this reaction. Promotion of 2 wt% Rh/SiO 2 by 1 wt% Fe produced a catalyst that exhibited a 22% selectivity to ethanol, with methane being the primary side-product. Addition of Fe to 2 wt% Rh/titania also improved the selectivity to ethanol with the highest selectivity being 37% for a sample with 5 wt% Fe. The effects of temperature, pressure and H 2:CO ratio on the performance of 2 wt% Rh/TiO 2 and 2 wt% Rh–2.5 wt% Fe/TiO 2 were also studied. Although the influence of pressure and H 2:CO ratio was moderate, higher temperatures clearly increased methane production at the expense of ethanol and methanol. Adsorption and thermal desorption of CO in Ar or H 2 were also studied by DRIFTS spectroscopy on 2 wt% Rh/TiO 2 and 2 wt% Rh–2.5 wt% Fe/TiO 2. The gem-dicarbonyl species that was the primary species on these catalysts at room temperature after exposure to CO was more thermally stable on the Fe-promoted catalyst.

Characterization and Reactivity of the Mo4S6+Cluster Deposited on Au(111)

Mass-selected cluster deposition was used to investigate the chemical and thermal properties of the Mo 4S 6 cluster deposited onto a Au(111) substrate. Auger spectroscopy and (13)CO thermal desorption measurements demonstrate that the clusters behave independently up to coverages of ∼0.15 ML, while at higher coverages, cluster crowding or island formation results in no net increase in Mo-atom adsorption sites. DFT calculations show that CO binding on the Mo-atom top site is strongly preferred over the side sites, with scaled binding energies in reasonable agreement with the experimentally derived binding energy of 0.7 eV. DFT calculations predict that the total adsorption energy for sequential addition of two CO molecules (top and side site) is nearly additive, whereas the addition of a third CO to another empty Mo side site is less stable. The latter is attributed to repulsive intercluster interactions and is consistent with the experimentally estimated sticking coefficient of 0.4 ± 0.1. In contrast to C...

Alloy Formation and CO Adsorption on Bimetallic Ca/Pd(111) Surfaces

Ca films deposited on the surface of Pd(111) were studied by temperature-programmed desorption, X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy, and low-energy electron diffraction (LEED). Multilayer Ca films desorb at 1180 K, which is much higher than that value for any of the alkali metals. Ca adatoms alloy with Pd at temperatures as low as 700 K. Annealing sub-monolayer Ca films at 1100 K reproducibly formed two well-ordered surface structures with (2 × 2) and (√3×√3)R30° Ca/Pd(111) unit cells depending on the amount of Ca deposited on the Pd(111) substrate. Chemical shifts of Ca XPS peaks indicate that these ordered structures are correlated to the formation of Ca−Pd alloys. The presence of Ca at the Pd(111) surface increases the CO adsorption energy and causes a 110-K shift of the CO thermal desorption peak to a higher temperature than from a clean Pd(111) surface. This Ca−Pd−CO interaction is so strong that it drives Ca out of a Ca−Pd alloyed layer to the overlayer upon CO adsorp...

Acetone condensation over molybdenum nitride and carbide catalysts

Acetone condensation was carried out over high surface area molybdenum nitride and carbide catalysts. Rates and selectivities for these materials were compared to those for MgO (a solid base catalyst), USY (a solid acid catalyst) and 1% Pt/SiO 2 (a supported noble metal catalyst). The Mo 2N catalyst as well as MgO and USY catalyzed the condensation of acetone to products including mesityl oxide (MO), mesitylene and isophorone. Areal rates for the Mo 2C and Mo 2N catalysts were higher than those for the MgO and USY catalysts. The Mo 2N catalyst was most active for mesityl oxide production. The formation of mesitylene and isophorone over this catalyst indicated that Mo 2N possessed strong acid and base sites, respectively. Results from the thermal desorption of CO 2 and NH 3 confirmed the presence of these sites. The hydrogenation of acetone to isopropanol (IPA) and its subsequent dehydration to propylene were predominant reactions for the Mo 2C and 1% Pt/SiO 2 catalysts. Differences between the Mo 2N and Mo 2C catalysts are explained based on their base, acid and metallic properties.

Reactivity of mixed rhodium/aluminium thin films deposited on gamma-alumina

Rh and Al mixed thin films deposited on the gamma-alumina surface were studied. Auger electron spectroscopy as well as thermal desorption spectroscopy (TDS) results showed significant alloying of Rh and Al after the first annealing of the system. CO thermal desorption results were strongly influenced by the previous CO adsorption–desorption cycles, showing strong CO adsorbate–induced reversible changes on the surface. TDS and molecular beam reactive scattering (CO oxidation) results depended on Rh:Al atomic ratio significantly. Shapes of CO oxidation curves were similar to the results obtained on clean Rh foil previously and their intensity also corresponded to Rh surface concentration.

An AES, XPS and TDS study on the growth and property of silver thin film on the Pt( [formula omitted])-(1×2) surface

Silver thin film growth on the Pt(1 1 0)-(1×2) surface was investigated by Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and CO thermal desorption spectroscopy at various temperatures. At room temperature, the silver thin film growth follows the Stranski–Krastanov mode, i.e., layer-by-layer growth up to 1.5 monolayer (ML) followed by 3D island growth. During the initial 1.5 ML layer-by-layer growth, the first 0.5 ML silver atoms fill in the missing-row sites of the Pt(1 1 0)-(1×2) surface and form a pseudo Pt(1 1 0)-(1×1)–0.5 ML Pt–0.5 ML Ag surface structure, then the subsequent and the last 0.5 ML silver atoms grow on the Ag sites and the Pt sites of the pseudo (1×1) surface, respectively. AES and XPS results reveal that the 3D Ag islands are not so stable as the 1.5 ML silver thin film. It is also found that interactions occur between Pt and Ag, in which electrons are transferred from Pt to Ag, causing the Ag 3d binding energy to shift to the lower binding energy, compared with that of bulk silver. At 600 K, the formation of surface Ag–Pt compound follows the 2.25 ML layer-by-layer growth of the silver thin film on Pt(1 1 0)-(1×2).