Coverage dependence of neopentane trapping dynamics on Pt(111)

Adsorption probabilities for neopentane on Pt(111) were measured directly using supersonic molecular-beam techniques at coverages ranging from zero to monolayer saturation, incident translational energies between 18 and 110 kJ mol⁻¹ and incident angles between 0° and 60° at a surface temperature of 105 K. The adsorption probability was found to increase with coverage up to near monolayer saturation at all incident translational energies and incident angles. The coverage dependence of the adsorption probability predicted by a modified Kisliuk model with enhanced trapping into the second layer exhibits good quantitative agreement with the experimental values. The angular dependence of the adsorption probability decreases with increasing coverage, suggesting that the effective corrugation of the gas–surface interaction potential increases with the adsorbate coverage. The initial adsorption probability into the second layer onto the covered surface decreases from 0.95 to 0.75 with increasing energy over the energy range studied, and exhibits total energy scaling. A comparison with second-layer trapping data of simpler molecules onto covered Pt(111) indicates that the structural complexity of adsorbed neopentane molecules facilitates collisional energy transfer during adsorption.     

Sulfur-induced mobilization of Au surface atoms on Au(1 1 1) studied by real-time STM

The interaction of sulfur with gold surfaces has attracted considerable interest due to numerous technological applications such as the formation of self-assembled monolayers and as a chemical sensor. Here, we report on the interaction of sulfur with Au(1 1 1) at two different temperatures (300 K and 420 K) studied by real-time scanning tunnelling microscopy, low energy electron diffraction and Auger electron spectroscopy. In the low coverage regime (<0.1 ML), S adsorption lifts the herringbone reconstruction of the clean Au(1 1 1) surface indicating a lateral expansion of the surface layer. An ordered (√3 × √3)R30° sulfur adlayer develops as the coverage reaches ∼0.3 ML. At higher S coverages (>0.3 ML) gold surface atoms are removed from regular terrace sites and incorporated into a growing gold sulfide phase. At 300 K this process leads to the formation of a rough pit and mound surface morphology. This gold sulfide exhibits short-range order and an incommensurate, long-range ordered AuS phase develops upon annealing at 450-525 K. In contrast, formation of an ordered AuS phase via rapid step-retraction rather than etch pit formation is observed during S-interaction with Au(1 1 1) surfaces at 420 K. Our results shed new light on the S-Au(1 1 1) interaction.     

TPD, HREELS and UPS study of the adsorption and reaction of methyl nitrite (CH3ONO) on Pt(111)

The adsorption and reaction of methyl nitrite (CH₃ONO, CD₃ONO) on Pt(111) was studied using HREELS, UPS, TPD, AES, and LEED. Adsorption of methyl nitrite on Pt(111) at 105 K forms a chemisorbed monolayer with a coverage of 0.25 ML, a physisorbed second layer with the same coverage that desorbs at 134 K, and a condensed multilayer that desorbs at 117 K. The Pt(111) surface is very reactive towards chemisorbed methyl nitrite; adsorption in the monolayer is completely irreversible. CH₃ONO dissociates to form NO and an intermediate which subsequently decomposes to yield CO and H₂ at low coverages and methanol for CH₃ONO coverages above one-half monolayer. We propose that a methoxy intermediate is formed. At least some C–O bond breaking occurs during decomposition to leave carbon on the surface after TPD. UPS and HREELS show that some methyl nitrite decomposition occurs below 110 K and all of the methyl nitrite in the monolayer is decomposed by 165 K. Intermediates from methyl nitrite decomposition are also relatively unstable on the Pt(111) surface since coadsorbed NO, CO and H are formed below 225 K.     

Adsorption of oxygen on Au(111) by exposure to ozone

Atomic oxygen coverages of up to 1.2 ML may be cleanly adsorbed on the Au(111) surface by exposure to O₃ at 300 K. We have studied the adsorbed oxygen layer by AES, XPS, HREELS, LEED, work function measurements and TPD. A plot of the O(519 eV)/Au(239 eV) AES ratio versus coverage is nearly linear, but a small change in slope occurs at Θ_O=0.9 ML. LEED observations show no ordered superlattice for the oxygen overlayer for any coverage studied. One-dimensional ordering of the adlayer occurs at low coverages, and disordering of the substrate occurs at higher coverages. Adsorption of 1.0 ML of oxygen on Au(111) increases the work function by +0.80 eV, indicating electron transfer from the Au substrate into an oxygen adlayer. The O(1s) peak in XPS has a binding energy of 530.1 eV, showing only a small (0.3 eV) shift to a higher binding energy with increasing oxygen coverage. No shift was detected for the Au 4f_7/2 peak due to adsorption. All oxygen is removed by thermal desorption of O₂ to leave a clean Au(111) surface after heating to 600 K. TPD spectra initially show an O₂ desorption peak at 520 K at low Θ_O, and the peak shifts to higher temperatures for increasing oxygen coverages up to Θ_O=0.22 ML. Above this coverage, the peak shifts very slightly to higher temperatures, resulting in a peak at 550 K at Θ_O=1.2 ML. Analysis of the TPD data indicates that the desorption of O₂ from Au(111) can be described by first-order kinetics with an activation energy for O₂ desorption of 30 kcal mol⁻¹ near saturation coverage. We estimate a value for the Au–O bond dissociation energy D(Au–O) to be 56 kcal mol⁻¹.     

Sb induced (7×7) to (1×1) surface phase transformation of the Si(111) surface

Adsorption of Sb at a very low flux rate results in an epitaxial layer-by-layer growth on Si(111) surface held at room-temperature. Band-bending is not observed for submonolayer Sb coverages while sharp changes in the photoemission features are observed for 1.0 monolayer (ML) Sb adsorption. Changes in the core level binding energy and width in X-ray photoelectron spectroscopy, surface related feature in Electron energy loss spectroscopy and spot intensity ratios in Low energy electron diffraction studies suggest a surface phase transition upon adsorption of 1.0 monolayer of Sb. A plausible model is proposed to explain the abrupt metal-semiconductor transformation at this critical coverage of 1.0 ML.     

Adsorption of hydrogen and carbon monoxide on Rh(1 1 1)/V surface alloys

A detailed study of the interaction of hydrogen and carbon monoxide with two different Rh(1 1 1)/V surface alloys (1/3 monolayer of V in the second atomic layer or 1/3 monolayer of V in form of islands on the surface) is presented in comparison to the clean Rh(1 1 1) surface. For hydrogen a decrease in the sticking coefficient is found for both alloy surfaces. The sticking coefficient of H₂ as a function of the translational energy is similar to the Rh(1 1 1) surface, showing a direct activated adsorption mechanism. For low translational energies hydrogen adsorption is dominated by dynamical steering on Rh(1 1 1) and by a precursor mechanism on the Rh(1 1 1)/V subsurface alloy. The H₂ TPD desorption peaks are shifted to lower temperatures on the alloy surfaces, caused by the downshift of the metal d-band due to V alloying. On all three surfaces the saturation coverage of hydrogen was measured, giving 1.2, 1.0 and 0.8 monolayer for Rh(1 1 1), the Rh(1 1 1)/V subsurface alloy and for the Rh(1 1 1)/V islands, respectively. For CO the sticking coefficients and the saturation coverages are basically the same on the Rh(1 1 1) and the alloy surfaces. There is an extrinsic precursor on the ordered CO (√3×√3) phase on the Rh(1 1 1) surface, but there is no evidence for such a precursor on the Rh(1 1 1)/V subsurface alloy. On the Rh(1 1 1)/V islands surface, the extrinsic precursor exists on the Rh(1 1 1) surface between the V islands. Apparently this precursor is only stable on the ordered CO layer on Rh(1 1 1).     

The adsorption of NO on an oxygen pre-covered Pt(1 1 1) surface: in situ high-resolution XPS combined with molecular beam studies

Adsorption of NO on a Pt(1 1 1) surface pre-covered with a p(2 × 2) atomic oxygen layer has been studied in situ by high-resolution X-ray photoelectron spectroscopy and temperature-programmed XPS using third-generation synchrotron radiation at BESSY II, Berlin, combined with molecular beam techniques and ex situ by low energy electron diffraction and temperature-programmed desorption. O 1s XP spectra reveal that an ordered p(2 × 2)-O layer dramatically changes the adsorption behavior of NO as compared to the clean surface. The atomic oxygen occupies fcc hollow sites, and therefore blocks NO adsorption on these sites, which are energetically preferred on clean Pt(1 1 1). As a consequence, NO populates on-top sites at low coverage. At 110 K for higher coverages, NO can additionally adsorb on hcp hollow sites, thereby inducing a shift of the O 1s binding energy of atomic oxygen towards lower energies by about 0.25 eV. The bond strength of the hcp hollow NO species to the substrate is weakened by the presence of atomic oxygen. A sharp p(2 × 2) LEED pattern is observed for NO adsorption on the oxygen pre-covered surface, up to saturation coverage. The total saturation coverage of NO on Pt(1 1 1) pre-covered with varying amounts of oxygen (below 0.25 ML) decreases linearly with the coverage of oxygen. The initial sticking coefficient of NO is reduced from 0.96 on clean Pt(1 1 1) to 0.88 on a p(2 × 2) oxygen pre-covered surface.     

Coverage-dependent molecular tilt of carbon monoxide chemisorbed on Pt{110}: A combined LEED and DFT structural analysis

The adsorption of carbon monoxide on the Pt{110} surface at coverages of 0.5 ML and 1.0 ML was investigated using quantitative low-energy electron diffraction (LEED IV) and density-functional theory (DFT). At 0.5 ML CO lifts the reconstruction of the clean surface but does not form an ordered overlayer. At the saturation coverage, 1.0 ML, a well-ordered p(2 × 1) superstructure with glide line symmetry is formed. It was confirmed that the CO molecules adsorb on top of the Pt atoms in the top-most substrate layer with the molecular axes tilted by ± 22° with respect to the surface normal in alternating directions away from the close packed rows of Pt atoms. This is accompanied by significant lateral shifts of 0.55 Å away from the atop sites in the same direction as the tilt. The top-most substrate layer relaxes inwards by ? 4% with respect to the bulk-terminated atom positions, while the consecutive layers only show minor relaxations. Despite the lack of long-range order in the 0.5 ML CO layer it was possible to determine key structural parameters by LEED IV using only the intensities of the integer-order spots. At this coverage CO also adsorbs on atop sites with the molecular axis closer to the surface normal (< 10°). The average substrate relaxations in each layer are similar for both coverages and consistent with DFT calculations performed for a variety of ordered structures with coverages of 1.0 ML and 0.5 ML.     

An STM investigation of the interaction and ordering of pentacene molecules on the Ag/Si(1 1 1)-(√3×√3)R30° surface

Scanning tunneling microscopy has been used to study the ordering of pentacene (C₂₂H₁₄) molecules on the Ag/Si(1 1 1)-(√3×√3)R30° surface at room temperature. Two solid phases, S1 and S2, are observed at coverages of ∼0.35 monolayer (ML) and ∼1.0 ML respectively. It is shown that the solid phase S1 has a high-order commensurate lattice, Ag/Si(1 1 1)-(25 × 25)-pentacene, containing 75 molecules. The structure of this phase is determined from STM measurements at very low coverages where it is possible to image both the pentacene molecules and the structure of the Ag/Si(1 1 1) substrate. Two adsorption sites are identified, a three-fold hollow site at the centre of a Ag-trimer (CA-site) and a six-fold hollow site at the centre of the hexagonal arrangement of silver atoms (CB-site). A higher pentacene coverage of ∼1 ML lead to a molecular reorganization and forms a new commensurate structure Ag/Si(1 1 1)-(2 × 3)-pentacene, containing two molecules per unit cell. Because low energy electron diffraction patterns were not obtainable for this system, the structure of this second phase is determined by using the bias voltage as a tunable parameter to “focus” on either the molecular film or on the substrate. In this phase adsorption takes place exclusively on the Ag-trimer (CA) site and the CB-site is lost because of strong lateral molecule-molecule interactions. The role of competition between intermolecular and molecule-substrate interactions and the nature of the adsorption sites in determining the structure of the pentacene layers is discussed.     

Adsorption of gas-phase oxygen atoms on Pt(1 0 0)-hex-R0.7°: Evidence of a metastable chemisorbed phase

We utilized temperature programmed desorption (TPD) and low energy electron diffraction (LEED) to study the chemisorption of gas-phase oxygen atoms on Pt(1 0 0)-hex-R0.7° at 450 K and 573 K, and find that the types and relative populations of oxygen phases that develop are highly dependent on the surface temperature during adsorption. At both temperatures, oxygen atoms initially adsorb on defects associated with the surface reconstruction. Increasing the coverage to about 0.32 ML (monolayers) at 573 K causes deconstruction and population of a phase with apparent (3 × 1) symmetry that desorbs in a single feature centered at about 672 K. Saturating at 0.63 ML leads to the formation of an additional “complex” ordered phase that desorbs in a sharp feature exhibiting autocatalytic behavior as it shifts from approximately 631 K to 642 K. Uptake at 450 K also initiates deconstruction, but in this case two desorption maxima at about 652 K and 672 K grow simultaneously with increasing coverage to about 0.32 ML. The feature at 672 K is associated with the disordered (3 × 1) phase, while the feature at 652 K has not been previously reported. We attribute this new feature to desorption from disordered arrangements of high oxygen concentrations on (1 × 1) surface regions. As the coverage increases to about 0.51 ML, small amounts of the complex phase grow, while this “high-concentration” (1 × 1) and the (3 × 1) phases continue to develop. We conclude that the complex phase is energetically preferred over the high-concentration (1 × 1) phase, but kinetic barriers hinder its formation at 450 K, causing oxygen to become trapped in the high-concentration (1 × 1) phase. Therefore, the high-concentration (1 × 1) phase is metastable relative to the complex phase. Lastly, above about 0.51 ML, further adsorption at 450 K promotes the growth of Pt oxide islands as detailed in a future investigation.     

Growth and electronic structure of Mn on Al(1 1 1)

Growth and electronic structure of a 3d transition metal Mn on a free-electron-like metal Al(1 1 1) have been studied by photoelectron spectroscopy and low energy electron diffraction (LEED). A LEED is observed at 6 ML Mn coverage, that is related to the α phase of bulk Mn. From the intensity of the adlayer and substrate core-level peaks and angle dependent studies, evidence of primarily layer by layer growth is observed. The Mn 2p core-level for 0.1 ML Mn coverage appears at 0.3 eV lower binding energy with respect to bulk Mn. With increasing Mn coverage, the Mn 2p binding energy increases. An extra component is observed at the lower binding energy side of the Al 2p spectra, that is related to interface alloying. The asymmetric line-shape of bulk-like Mn becomes symmetric for lower Mn coverages.     

Anomalous adsorption of Cs on Pt(1 1 1)

The adsorption of Cs on Pt(1 1 1) surfaces and its reactivity toward oxygen and iodine for coverages θ_Cs?0.15 is reported. These surfaces show unusual “anomalous” behavior compared to higher coverage surfaces. Similar behavior of K on Pt(1 1 1) was previously suggested to involve incorporation of K into the Pt lattice. Despite the larger size of Cs, similar behavior is reported here. Anomalous adsorption is found for coverages lower than 0.15 ML, at which point there is a change in the slope of the work function. Thermal Desorption Spectroscopy (TDS) shows a high-temperature Cs peak at 1135 K, which involves desorption of Cs⁺ from the surface.The anomalous Cs surfaces and their coadsorption with oxygen and iodine are characterized by Auger Electron Spectroscopy (AES), TDS and Low Electron Energy Diffraction (LEED). Iodine adsorption to saturation on Pt(1 1 1)(anom)-Cs give rise to a sharp LEED pattern and a distinctive work function increase. Adsorbed iodine interacts strongly with the Cs and weakens the Cs-Pt bond, leading to desorption of Cs_xI_y clusters at 560 K. Anomalous Cs increases the oxygen coverage over the coverage of 0.25 ML found on clean Pt. However, the Cs-Pt bond is not significantly affected by coadsorbed oxygen, and when oxygen is desorbed the anomalous cesium remains on the surface.     

Core level photoemission and STM characterization of Ta/Si(1 1 1)-7 × 7 interfaces

We present the results of scanning tunneling microscopy (STM) and photoemission spectroscopy (PES) of the Ta/Si(1 1 1)-7 × 7 system after deposition of Ta at substrate temperatures from 300 to 1250 K. The coverage of Ta varied from 0.05 up to 2.5 of a monolayer (ML). STM shows that at 300 K and coverage less than 1 ML, a disordered chemisorbed phase is formed. Deposition on a hot surface (above 500 K) produces round 3D clusters randomly distributed on the surface. Cluster height and their diameter are found to change drastically with annealing temperature and the Ta coverage. Analysis of photoemission data of the Si 2p core levels shows that at room temperature and at coverage ?1 ML core level binding energy shifts and intensity variations of Si surface related components are observed, which clearly indicate that the reaction starts already at 300 K. Shifts in the binding energy, changes of the peak shapes and intensity of the Ta 4f doublet at higher temperatures can be explained by the formation of stable silicide on the surface.     

Metastable structures of Dy layers adsorbed on Mo(112) and their transformations

Ordering of dysprosium on Mo(112) up to 1.5 monolayers has been investigated by LEED and work function analysis after adsorption at 100 K and annealing between 200 and 1000 K. At low annealing temperatures (< 350-600 K) ordered structures are found, which are changed or even destroyed irreversibly by annealing steps to higher temperatures. At coverages, θ, up to 0.3 monolayer a (6×1) not strictly commensurate chain structure is seen, which coexists up to θ = 0.58 with a one-dimensionally incommensurate c( 1.56×2) structure. At higher coverages up to the physical monolayer at θ≈ 0.77, incommensurate ( n×2) followed by oblique ( n×1) structures are seen with n continuously variable with coverage. The second layer forms a p (1.33×1) structure. Annealing to higher temperatures causes irreversible structural transitions with strongly coverage dependent properties. Up to θ = 0.58, only a glass-like disordered phase is formed, which cannot be ordered again. In contrast, the rectangular incommensurate structures between 0.58 < θ < 0.68 remain unchanged upon annealing, whereas the structures at higher coverages and those of the second layer are transformed into commensurate (s×1) structures with integer s. Geometrical models are presented for the non-annealed structures and possible origins for the two-dimensional concentration dependent vitrification of the Dy layers are discussed. Received 15 June 2001     

Structural evolution at the initial growth stage of perylene on Au(1 1 1)

We report on the structural evolution at the initial growth stage of perylene thin films on Au(1 1 1) surface. Scanning tunneling microscopy and spectroscopy have been employed to investigate the structural and electronic properties at 78 K. Rapid molecular diffusion was observed at low submonolayer coverage. Molecules form an ordered structure at monolayer coverage. For the second layer, impinging molecules nucleate into molecular islands with an ordered intermediate structure.     

Scanning tunneling microscopy and spectroscopy investigations of copper phthalocyanine adsorbed on Al2O3/Ni3Al(1 1 1)

Low temperature scanning tunneling microscopy (LT-STM) and scanning tunneling spectroscopy (STS) have been used to investigate adsorbed copper phthalocyanine (C₃₂H₁₆N₈Cu) molecules on an ordered ultrathin Al₂O₃ film on the Ni₃Al(1 1 1) surface as a function of coverage and annealing temperature. For sub-monolayer coverage and a deposition temperature of 140 K two different planar molecular adsorption configurations rotated by 30° with respect to each other were observed with submolecular resolution in the STM images. The template effect of the underlying oxide film on the CuPc orientation, however, is only weak and negligible at higher coverages. For θ_CuPc ≈ 1 ML, before completion of the first layer, the growth of a second layer was already observed. The measured spacing of 3.5 Å between first and second layer corresponds to the distance between the layers in the α-modification of crystalline CuPc. The molecules deposited at 140 K are thermally stable upon prolonged annealing to temperatures up to 250 K. By the use of STS the lowest unoccupied molecular orbital (LUMO) of the adsorbed copper phthalocyanine molecules has been identified at an energy of 1.2 eV above E_F. The lateral distribution of the electronic states of the CuPc has been analyzed and mapped by STS.     

Potassium adsorption on graphite(0001)

Potassium adsorption on graphite has been studied with emphasis on the two-dimensional K adlayer below one monolayer. Data are presented for the work function versus coverage, high-resolution electron energy loss spectroscopy (HREELS) vibrational spectra of K-adlayers, low energy electron diffraction and ultraviolet photoemission spectroscopy (UPS) spectra at different coverages. The data provide information regarding the vibrational properties of the K-adlayer, the metallization of the adlayer at submonolayer coverages, and the charge transfer from the K adatoms to the graphite substrate. Analysis of the work function, HREELS, and UPS data provides a qualitatively consistent picture of the charge state of the K adatoms, where at low coverages, below a critical coverage θ_c (θ_c=0.2–0.3), the K adatoms are dispersed and (partially) ionized, whereas at θ>θ_c islands of a metallic 2×2 K phase develops that coexist with the dispersed a K adatoms up to θ=1. We show that it is possible to understand the variation of the work function data based on a two-phase model without invoking a depolarization mechanism of adjacent dipoles, as is normally done for alkali-metal adsorption on metal surfaces. Similarly, the intensity variation as a function of coverage of the energy loss peak at 17 meV observed in HREELS, and the photoemission peak at E_b=0.5 eV seen in UPS can be understood from a two-phase model. A tentative explanation is presented that connects apparent discrepancies in the literature concerning the electronic structure of the K adlayer. In particular, a new assignment of the K-induced states near the Fermi level is proposed.     

Hexaphenyl thin films on clean and carbon covered Au(1 1 1) studied with TDS and LEED

The adsorption and growth of ordered para-hexaphenyl (6P) films have been investigated both on clean and partially carbon pre-covered Au(1 1 1) single crystal surfaces by thermal desorption spectroscopy (TDS) and low energy electron diffraction (LEED) under ultra-high vacuum conditions. The existence of a distinct first and second monomolecular 6P layer that clearly separate from the multilayer regime, which comprise lying molecules with respect to the substrate surface, could be inferred from TDS. For both the 6P mono- and multilayer grown on pure Au(1 1 1) the desorption energies have been determined based on experimental TDS data. In particular, for the monolayer regime a coverage dependence of the desorption energy has been found, which is attributed to repulsive interactions between neighbouring 6P molecules adsorbed on the gold surface. The existence of well-ordered film structures could be inferred from LEED for half monolayer and full monolayer thick 6P films. Based on the LEED and TDS data, structural models are presented for these highly ordered organic films. Multi-step dehydrogenation of 6P molecules adsorbed on clean Au(1 1 1) surfaces is reported for temperatures above 650 K together with experimental evidence for the existence of a regular overlayer composed of partially dehydrogenated polycyclic aromatic hydrocarbon (PAH) intermediates. A quite different adsorption/desorption kinetics and film growth has been observed for 6P films grown on carbon pre-covered Au(1 1 1) surfaces.     

Growth of epitaxial thin Pd(1 1 1) films on Pt(1 1 1) and oxygen-terminated FeO(1 1 1) surfaces

Thin Pd films (1-10 monolayers, ML) were deposited at 35 K on a Pt(1 1 1) single crystal and on an oxygen-terminated FeO(1 1 1) monolayer supported on Pt(1 1 1). Low energy electron diffraction, Auger electron spectroscopy, and Kr and CO temperature programmed desorption techniques were used to investigate the annealing induced changes in the film surface morphology. For growth on Pt(1 1 1), the films order upon annealing to 500 K and form epitaxial Pd(1 1 1). Further annealing above 900 K results in Pd diffusion into the Pt(1 1 1) bulk and Pt-Pd alloy formation. Chemisorption of CO shows that even the first ordered monolayer of Pd on Pt(1 1 1) has adsorption properties identical to bulk Pd(1 1 1). Similar experiments conducted on FeO(1 1 1) indicate that 500 K annealing of a 10 ML thick Pd deposit also yields ordered Pd(1 1 1). In contrast, annealing of 1 and 3 ML thick Pd films did not result in formation of continuous Pd(1 1 1). We speculate that for these thinner films Pd diffuses underneath the FeO(1 1 1).     

Glycine on Pt(111): a TDS and XPS study

The adsorption and desorption of in situ deposited glycine on Pt(111) were investigated with thermal desorption spectroscopy (TDS) and X-ray photoelectron spectroscopy (XPS). Glycine adsorbs intact on Pt(111) at all coverages at temperatures below 250 K. The collected results suggest that the glycine molecules adsorb predominantly in the zwitterionic state both in the first monolayer and in multilayers. Upon heating, intact molecules start to desorb from multilayers around 325 K. The second (and possibly third) layer(s) are somewhat more strongly bound than the subsequent layers. The multilayer desorption follows zero order kinetics with an activation energy of 0.87 eV molecule⁻¹. From the first saturated monolayer approximately half of the molecules desorbs intact with a desorption peak at 360 K, while the other half dissociates before desorption. Below 0.25 monolayer all molecules dissociate upon heating. The dissociation reactions lead to H₂, CO₂, and H₂O desorption around 375 K and CO desorption around 450 K. This is well below the reported gas phase decomposition temperature of glycine, but well above the thermal desorption temperatures of the individual H₂, CO₂, and H₂O species on Pt(111), i.e. the dissociation is catalyzed by the surface and H₂, CO₂, and H₂O immediately desorb upon dissociation. For temperatures above 500 K the remaining residues of the dissociated molecules undergo a series of reactions leading to desorption of, for example, H₂CN, N₂ and C₂N₂, leaving only carbon left on the surface at 900 K. Comparison with previously reported studies of this system show substantial agreement but also distinct differences.