Metal organic chemical vapor deposition of ultrathin ZrO2 films on Si(1 0 0) and Si(1 1 1) studied by electron spectroscopy

The growth of ultrathin ZrO₂ films on Si(1 0 0)-(2 × 1) and Si(1 1 1)-(7 × 7) has been studied with core level photoelectron spectroscopy and X-ray absorption spectroscopy. The films were deposited sequentially by chemical vapor deposition in ultra-high vacuum using zirconium tetra-tert-butoxide as precursor. Deposition of a > 50 Å thick film leads in both cases to tetragonal ZrO₂ (t-ZrO₂), whereas significant differences are found for thinner films. On Si(1 1 1)-(7 × 7) the local structure of t-ZrO₂ is not observed until a film thickness of 51 Å is reached. On Si(1 0 0)-(2 × 1) the local geometric structure of t-ZrO₂ is formed already at a film thickness of 11 Å. The higher tendency for the formation of t-ZrO₂ on Si(1 0 0) is discussed in terms of Zr-O valence electron matching to the number of dangling bonds per surface Si atom. The Zr-O hybridization within the ZrO₂ unit depends furthermore on the chemical composition of the surrounding. The precursor t-butoxy ligands undergo efficient C-O scission on Si(1 0 0), leaving carbonaceous fragments embedded in the interfacial layer. In contrast, after small deposits on Si(1 1 1) stable t-butoxy groups are found. These are consumed upon further deposition. Stable methyl and, possibly, also hydroxyl groups are found on both surfaces within a wide film thickness range.     

Surface reactions of 2-iodopropane on GaAs(1 0 0)

The surface reactions of 2-iodopropane ((CH₃)₂CHI) on gallium-rich GaAs(1 0 0)-(4 × 1), was studied by temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). CH₃CHICH₃ adsorbs molecularly at 120 K but dissociates below room temperature to form chemisorbed 2-propyl ((CH₃)₂CH) and iodide (I) species. Thermal activation causes desorption of the molecular species at 240 K, and this occurs in competition with the further reactions of the (CH₃)₂CH and I chemisorbed species. Self-coupling of the (CH₃)₂CH results in the formation of 2,3-dimethylbutane ((CH₃)₂CH-CH(CH₃)₂) at 290 K. β-Hydride elimination in (CH₃)₂CH yields gaseous propene (CH₃CHCH₂) at 550 K while reductive elimination reactions of (CH₃)₂CH with surface hydrogen yields propane (CH₃CH₂CH₃) at 560 K. Recombinative desorption of the adsorbed hydrogen as H₂ also occurs at 560 K. We observe that the activation barrier to carbon-carbon bond formation with 2-propyls on GaAs(1 0 0) is much lower than that in our previous investigations involving ethyl and 1,1,1-trifluoroethyl species where the β-elimination process was more facile. The difference in the surface chemistry in the case of 2-propyl species is attributable to its rigid structure resulting from the bonding to the surface via the second carbon atom, which causes the methyl groups to be further away from the surface than in the case of linear ethyl and 1,1,1-trifluoroethyl species. The β-hydride and reductive elimination processes in the adsorbed 2-propyl species thus occurs at higher temperatures, and a consequence of this is that GaI desorption, which is expected to occur in the temperature range 550-560 K becomes suppressed, and the chemisorbed iodine leaves the surface as atomic iodine.     

Soft X-ray appearance potential spectroscopy (SXAPS) study of TiO2(1 1 0)-1 × 2 and (0 0 1)-1 × 1 surfaces

A soft X-ray appearance potential spectroscopy (SXAPS) apparatus with high sensitivity was built to measure non-derivative spectra. SXAPS spectra (non-derivative) of Ti 2p and O 1s for TiO₂(1 1 0)-1 × 2 and (0 0 1)-1 × 1 surfaces have been measured using low incident currents (about 10 μA/cm²) and a photon counting mode. Density of empty states on Ti and O sites are deduced by self-deconvoluting the spectra. The self-deconvoluted SXAPS spectra are qualitatively similar to those measured by X-ray absorption spectroscopy (XAS). The Ti 2p_3/2 spectrum shows two strong peaks which correspond to t_2g and e_g states. For the O 1s spectrum two strong peaks near the threshold are also found which can be ascribed to O 2pπ and O 2pσ states. These results suggest that the spectra almost obey the dipole selection rule, so-called the “approximate dipole selection rule”. The SXAPS spectra of Ti 2p and O 1s for the (1 1 0) and (0 0 1) surfaces resemble qualitatively, which is consistent with the XAS results. The spectra measured on the (1 1 0)-1 × 2 surface at an incident angle of 45° off normal to the surface and on the (1 1 0) surface sputtered by Ar ions indicate that SXAPS is very sensitive to the surface electronic states.     

Oxygen-induced nano-faceting of Ir(2 1 0)

The adsorption of oxygen and the nanometer-scale faceting induced by oxygen have been studied on Ir(2 1 0). Oxygen is found to chemisorb dissociatively on Ir(2 1 0) at room temperature. The molecular desorption process is complex, as revealed by a detailed kinetic analysis of desorption spectra. Pyramid-shaped facets with {3 1 1} and (1 1 0) orientations are formed on the oxygen-covered Ir(2 1 0) surface when annealed to T?600 K. The surface remains faceted for substrate temperatures T<850 K. For T>850 K, the substrate structure reverts to the oxygen-covered (2 1 0) planar state and does so reversibly, provided that oxygen is not lost due to desorption or via chemical reactions upon which the planar (2 1 0) structure remains. A clean faceted surface was prepared through the use of low temperature surface cleaning methods: using CO oxidation, or reaction of H₂ to form H₂O, oxygen can be removed from the surface while preserving (“freezing”) the faceted structure. The resulting clean faceted surface remains stable for T<600 K. For temperatures above this value, the surface irreversibly relaxes to the planar state.     

Adsorption of water on thin V2O3(0 0 0 1) films

V₂O₃(0 0 0 1) films have been grown epitaxially on Au(1 1 1) and W(1 1 0). Under typical UHV conditions these films are terminated by a layer of vanadyl groups as has been shown previously [A.-C. Dupuis, M. Abu Haija, B. Richter, H. Kuhlenbeck, H.-J. Freund, V₂O₃(0 0 0 1) on Au(1 1 1) and W(1 1 0): growth, termination and electronic structure, Surf. Sci. 539 (2003) 99]. Electron irradiation may remove the oxygen atoms of this layer. H₂O adsorption on the vanadyl terminated surface and on the reduced surface has been studied with thermal desorption spectroscopy (TDS), vibrational spectroscopy (IRAS) and electron spectroscopy (XPS) using light from the BESSY II electron storage ring in Berlin. It is shown that water molecules interact only weakly with the vanadyl terminated surface: water is adsorbed molecularly and desorbs below room temperature. On the reduced surface water partially dissociates and forms a layer of hydroxyl groups which may be detected on the surface up to T ∼ 600 K. Below ∼330 K also co-adsorbed molecular water is detected. The water dissociation products desorb as molecular water which means that they recombine before desorption. No sign of surface re-oxidation could be detected after desorption, indicating that the dissociation products desorb completely.     

Core-level shifts at the Pt/W(1 1 0) monolayer bimetallic interface

We have measured W and Pt 4f_7/2 core-level photoemission spectra from interfaces formed by ultrathin Pt layers on W(1 1 0), completing our core-level measurements of W(1 1 0)-based bimetallic interfaces involving the group-10 metals Ni, Pd, and Pt. With increasing Pt coverage the sequence of W spectra can be described using three interfacial core-level peaks with binding-energy (BE) shifts (compared to the bulk) of −0.220 ± 0.015, −0.060 ± 0.015, and +0.110 ± 0.010 eV. We assign these features to 1D, 2D pseudomorphic (ps), and 2D closed-packed (cp) Pt phases, respectively. For ∼1 ps ML the Pt 4f_7/2 BE is 71.40 ± 0.02 eV, a shift of +0.46 ± 0.09 eV with respect to the BE of bulk Pt metal. The W 4f_7/2 core-level shifts induced by all three adsorbates are semiquantitatively described by the Born-Haber-cycle based partial-shift model of Nilsson et al. [39]. As with Ni/W(1 1 0), the difference in W 4f_7/2 binding energies between ps and cp Pt phases has a large structural contribution. The Pt 4f lineshape is consistent with a small density of states at the Fermi level, reflective of the Pt monolayer having noble-metal-like electronic structure.     

Oxidation of ultrathin indium layers on W(1 1 0)--a core-level photoemission study

We have studied the reaction of ultrathin In overlayers on W(1 1 0) with molecular oxygen at 300 K. At a coverage of 0.25 monolayers (ML) oxygen first chemisorbs dissociatively at free tungsten sites and oxidation of In occurs with some delay. At an In coverage of 1.2 ML complete oxidation of the closed overlayer is observed. Layers of 3 ML thickness first show rapid transformation from In to an In₂O₃-like species until an oxide monolayer is formed. Further oxidation occurs at much reduced rate. No oxygen-induced restructuring is observed for In at 300 K, in contrast to the response of Ag monolayers deposited on W(1 1 0).     

Ultrathin ZrO2 films on Si-rich SiC(0 0 0 1)-(3 × 3): Growth and thermal stability

The growth and thermal stability of ultrathin ZrO₂ films on the Si-rich SiC(0 0 0 1)-(3 × 3) surface have been explored using photoelectron spectroscopy (PES) and X-ray absorption spectroscopy (XAS). The films were grown in situ by chemical vapor deposition using the zirconium tetra tert-butoxide (ZTB) precursor. The O 1s XAS results show that growth at 400 °C yields tetragonal ZrO₂. An interface is formed between the ZrO₂ film and the SiC substrate. The interface contains Si in several chemically different states. This gives evidence for an interface that is much more complex than that formed upon oxidation with O₂. Si in a 4+ oxidation state is detected in the near surface region. This shows that intermixing of SiO₂ and ZrO₂ occurs, possibly under the formation of silicate. The alignment of the ZrO₂ and SiC band edges is discussed based on core level and valence PES spectra. Subsequent annealing of a deposited film was performed in order to study the thermal stability of the system. Annealing to 800 °C does not lead to decomposition of the tetragonal ZrO₂ (t-ZrO₂) but changes are observed within the interface region. After annealing to 1000 °C a laterally heterogeneous layer has formed. The decomposition of the film leads to regions with t-ZrO₂ remnants, metallic Zr silicide and Si aggregates.     

Hydrogen desorption kinetics and band bending for 6H-SiC(0 0 0 1) surfaces

The desorption kinetics of hydrogen from polished 6H-SiC(0 0 0 1) surfaces exposed to various sources of hydrogen have been determined using temperature programmed desorption (TPD). For (3 × 3) 6H-SiC(0 0 0 1) surfaces prepared via annealing and cooling in SiH₄, desorption of 0.2 ± 0.05 monolayer of molecular hydrogen was observed to occur at ≈590 °C. This β₁ H₂ desorption peak exhibited second order kinetics with an activation energy of 2.4 ± 0.2 eV. For (3 × 3) 6H-SiC surfaces exposed to atomic hydrogen generated via either a hot rhenium filament or remote hydrogen plasma, low energy electron diffraction patterns showed an eventual conversion back to (1 × 1) symmetry. Spectra acquired using Auger electron and X-ray photoelectron spectroscopies revealed that the atomic hydrogen exposure removed the excess Si. Photoelectron spectroscopy results also showed a 0.5 eV increase in binding energy for the Si2p and C1s core levels after removal of the Si-Si bilayer that is indicative of a decrease in band bending at the SiC surface. TPD from the (3 × 3) 6H-SiC(0 0 0 1) surfaces exposed to atomic hydrogen showed substantially more molecular hydrogen desorption (1-2 ML) through the appearance of a new desorption peak (β_2,3) that started at ≈200 °C. The β_2,3 peak exhibited second order desorption kinetics and a much lower activation energy of 0.6 ± 0.2 eV. A third smaller hydrogen desorption state was also detected in the 650-850 °C range. This last feature could be resolved into two separate desorption peaks (α₁ and α₂) both of which exhibited second order kinetics with activation energies of 4.15 ± 0.15 and 4.3 ± 0.15 eV, respectively. Based on comparisons to hydrogen desorption from Si and diamond surfaces, the β and α desorption peaks were assigned to hydrogen desorption from Si and C sites, respectively.     

Chemically prepared well-ordered InP(0 0 1) surfaces

In the present work HCl-isopropanol treated and vacuum annealed InP(0 0 1) surfaces were studied by means of low-energy electron diffraction (LEED), soft X-ray photoemission (SXPS), and reflectance anisotropy (RAS) spectroscopies. The treatment removes the natural oxide and leaves on the surface a physisorbed overlayer containing InCl_x and phosphorus. Annealing at 230 °C induces desorption of InCl_x overlayer and reveals a P-rich (2 × 1) surface. Subsequent annealing at higher temperature induces In-rich (2 × 4) surface. The structural properties of chemically prepared InP(0 0 1) surfaces were found to be similar to those obtained by decapping of As/P-capped epitaxial layers.     

Adsorption of iso-butane on ZnO(0 0 0 1)-Zn

Presented are thermal desorption spectroscopy (TDS) and adsorption probability measurements of iso-butane on the Zn-terminated surface of ZnO. The initial adsorption probability, S₀, decreases linearly from 0.57 to 0.22 (±0.02) with impact energy, E_i = 0.74-1.92 eV, and is independent of adsorption temperature, T_s = 91-114 K (±5 K), indicating non-activated molecular adsorption. The coverage, Θ, dependent adsorption probabilities, S(Θ), show a cross-over from adsorbate-assisted adsorption (S increases with Θ) to Kisliuk-like dynamics at about the desorption temperature of iso-butane bi-layers (∼110 K). Thus, the adsorption dynamics are precursor-mediated. The enhanced (gas-surface) mass-match, caused by forming a second layer of the alkane, leads to adsorbate-assisted adsorption. A direct fitting procedure of the TDS data yields a pre-exponential factor of 2.5 × 10¹³/s and a coverage dependent heat of adsorption of E_d(Θ) = 39 − 6 ∗ Θ + 2.5 ∗ exp(−Θ/0.07) kJ/mol.     

Thermally-induced morphological transition in WOx deposited on a ZrO2(1 0 0) substrate

A combined atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) study of tungsten oxide model catalysts is presented. The model catalysts were prepared by applying the real preparation method to a ZrO₂(1 0 0) single crystal support. AFM imaged several granular structures of scattered dimensions on the surface of ZrO₂(1 0 0) in the as prepared samples. After heating, at low loading the tungsten species rearranged into small WO_x particles strongly interacting with the substrate. At high tungsten content large WO₃ aggregates also formed. XPS analysis confirmed these changes. The estimated surface density of the interacting W-containing species closely matched that of real catalysts.     

Formation of vinylidene and vinylene by selective reactivity of Si(1 0 0)2 × 1 towards iso, cis and trans isomers of dichloroethylene

The room temperature (RT) chemisorption of three (iso, cis and trans) isomers of dichloroethylene (DCE) on Si(1 0 0)2 × 1 have been investigated by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). Unlike ethylene, the lack of molecular desorption features in the TPD data effectively rules out the cycloaddition adsorption mechanism for all three isomers. XPS spectra show that cis- and trans-DCE adsorb dissociatively on the 2 × 1 surface in equal proportion as mono-σ bonded 2-chlorovinyl and di-σ bonded vinylene adspecies, which could be produced by dechlorination mechanisms involving the proposed tri-atom π-complex and diradical intermediates, respectively. Acetylene (m/z 26) evolution from 2-chlorovinyl adspecies at 590 K and vinylene at 750 K are also observed for both cis- and trans-DCE, further confirming the common adsorption mechanisms for these geometrical isomers and the relative stabilities of the adspecies. In contrast, only vinylidene adspecies is found for iso-DCE, which indicates that the high ionicity of the CCl₂ group favours the diradical dechlorination mechanism. The single m/z 26 desorption peak for iso-DCE adspecies observed at a higher temperature (780 K) than cis and trans isomers is consistent with the higher adsorption energy of vinylidene than vinylene on Si(1 0 0) obtained in our ab initio calculations. The different relative locations of the Cl atoms in these isomers therefore play a crucial role in controlling the adsorption and thermal evolution on Si(1 0 0)2 × 1. The selective reactivity of the 2 × 1 surface towards these isomers can be used to generate vinylene or vinylidene templates from their corresponding adspecies.     

Characterization of methylidyne on Pt(1 1 1) with infrared spectroscopy

Methylidyne (CH) was prepared on Pt(1 1 1) by three methods: thermal decomposition of diiodomethane (CH₂I₂), ethylene decomposition at temperatures above 450 K, and surface carbon hydrogenation. Methylidyne and its precursors are characterized by reflection absorption infrared spectroscopy (RAIRS). The C-I bond of diiodomethane breaks upon adsorption to produce methylene (CH₂), which decomposes to methylidyne at temperatures above 130 K. Above 200 K, methylidyne is the only hydrocarbon species observed with RAIRS, although reaction channels for the formation of methane (CH₄) and ethylene (C₂H₄) are indicated by temperature programmed desorption (TPD). As is well known from numerous previous studies, ethylene decomposes to ethylidyne (CCH₃) upon exposure to Pt(1 1 1) at 410 K. Upon annealing to 450 K, ethylidyne dissociates through two reaction pathways, dehydrogenation to ethynyl (CCH) and C-C bond scission to methylidyne. Ethylene dehydrogenation on the surface at 750 K and under low ethylene exposures produces surface carbon that can be hydrogenated to methylidyne with C-H and C-D stretch frequencies of 2956 and 2206 cm⁻¹, respectively. Hydrogen co-adsorption on the surface causes these frequencies to shift to higher values. Methylidyne is stable on Pt(1 1 1) to temperatures up to 500 K.     

Surface chemistry of NO and NO2 on the Pt(1 1 0)-(1 × 2) surface: A comparative study

The surface chemistry of NO and NO₂ on clean and oxygen-precovered Pt(1 1 0)-(1 × 2) surfaces were investigated by means of high resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS). At room temperature, NO molecularly adsorbs on Pt(1 1 0), forming linear NO(a) and bridged NO(a). Coverage-dependent repulsive interactions within NO(a) drive the reversible transformation between linear and bridged NO(a). Some NO(a) decomposes upon heating, producing both N₂ and N₂O. For NO adsorption on the oxygen-precovered surface, repulsive interactions exist between precovered oxygen adatoms and NO(a), resulting in more NO(a) desorbing from the surface in the form of linear NO(a). Bridged NO(a) experiences stronger repulsive interactions with precovered oxygen than linear NO(a). The desorption activation energy of bridged NO(a) from oxygen-precovered Pt(1 1 0) is lower than that from clean Pt(1 1 0), but the desorption activation energy of linear NO(a) is not affected by the precovered oxygen. NO₂ decomposes on Pt(1 1 0)-(1 × 2) surface at room temperature. The resulted NO(a) (both linear NO(a) and bridged NO(a)) and O(a) repulsively interact each other. Comparing with NO/Pt(1 1 0), more NO(a) desorbs from NO₂/Pt(1 1 0) as linear NO(a), and both linear NO(a) and bridged NO(a) exhibit lower desorption activation energies. The reaction pathways of NO(a) on Pt(1 1 0), desorption or decomposition, are affected by their repulsive interactions with coexisting oxygen adatoms.     

The effect of ferroelectric polarization on the interaction of water and methanol with the surface of LiNbO3(0 0 0 1)

Water and methanol temperature programmed desorption (TPD) measurements were performed on the positive (c⁺) and negative (c⁻) surfaces of poled ferroelectric lithium niobate (LiNbO₃) single crystals. The results indicate that the molecule-surface interactions are both coverage and polarization-dependent. From a comparison of the TPD spectra for the positive and negative surfaces, it is shown that the desorption temperatures of water and methanol are consistently lower on the negative surface by 15 K and 20 K, respectively. The TPD spectra were simulated using the Polanyi-Wigner equation with a coverage-dependent energy term. These calculations show that the polarization dependence of the desorption temperature is due to a difference in the zero-coverage desorption energies on the two surfaces equal to a few kJ per mole. The mechanism for the polarization effect is explored with in situ pyroelectric voltage measurements, which indicate that a surface voltage of ±2 mV develops in the LiNbO₃(0 0 0 1) samples during TPD measurements. The magnitude of the pyroelectric-induced surface charge is heating rate dependent.     

Analysis of the first triad of interacting states (0 2 0), (1 0 0), and (0 0 1) of D2O from hot emission spectra

The far-infrared and middle-infrared emission spectra of deuterated water vapour were measured at temperatures 1370, 1520, and 1940 K in the ranges 320-860 and 1750-3400 cm⁻¹. The measurements were performed in an alumina cell with an effective length of hot gas of about 50 cm. More than 3550 new measured lines for the D₂¹⁶O molecule corresponding to transitions from highly excited rotational levels of the (0 2 0), (1 0 0), and (0 0 1) vibrational states are reported. These new lines correspond to rotational states with higher values of the rotational quantum numbers compared to previously published determinations: J_max = 29 and K_a(max) = 22 for the (0 2 0) state, J_max = 29 and K_a(max) = 25 for the (1 0 0) state, and J_max = 30 and K_a(max) = 23 for the (0 0 1) state. The extended set of 1987 experimental rotational energy levels for the (0 2 0), (1 0 0), and (0 0 1) vibration states including all previously available data has been determined. For the data reduction we used the generating function model. The root mean square (RMS) deviation between observed and calculated values is 0.004 cm⁻¹ for 1952 rovibrational levels of all three vibration states. A comparison of the observed energy levels with the best available values from the literature and with the global predictions from molecular electronic potential energy surfaces of water isotopic species [H. Partridge, D.W. Schwenke, J. Chem. Phys. 106 (1997) 4618] is discussed. The latter confirms a good consistency of mass-dependent DBOC corrections in the PS potential function with new experimental rovibrational data.     

Surface chemistry of HfI4 on Si(1 0 0)-(2 × 1) studied by core level photoelectron spectroscopy

The chemistry of HfI₄ adsorbed on the Si(1 0 0)-(2 × 1) surface has been studied by core level photoelectron spectroscopy in ultra-high vacuum. Two stable surface intermediates are identified: HfI₃ and HfI₂, both of which remain upon heating to 690 K. The dissociation of HfI₄ is accompanied by the formation of SiI. In addition, HfI₄ is observed up to 300 K. Complete desorption of iodine occurs in the temperature regime 690-780 K. Deposition of HfI₄ at 870 K results in a layer consisting of metallic Hf, whereas deposition at 1120 K results in the formation of Hf silicide. The results indicate that the metallic Hf formed at 870 K is in the form of particles. Oxidation of this film by O₂ at low pressure does not result in complete Hf oxidation. This suggests that complete oxidation of Hf is a critical step when using HfI₄ as precursor in atomic layer deposition.     

Formation and hydrogenation of p(2 × 2)-N on Pt(1 1 1)

The formation of a well-ordered p(2 × 2) overlayer of atomic nitrogen on the Pt(1 1 1) surface and its reaction with hydrogen were characterized with reflection absorption infrared spectroscopy (RAIRS), temperature programmed desorption (TPD), low energy electron diffraction (LEED), Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS). The p(2 × 2)-N overlayer is formed by exposure of ammonia to a surface at 85 K that is covered with 0.44 monolayer (ML) of molecular oxygen and then heating to 400 K. The reaction between ammonia and oxygen produces water, which desorbs below 400 K. The only desorption product observed above 400 K is molecular nitrogen, which has a peak desorption temperature of 453 K. The absence of oxygen after the 400 K anneal is confirmed with AES. Although atomic nitrogen can also be produced on the surface through the reaction of ammonia with an atomic, rather than molecular, oxygen overlayer at a saturation coverage of 0.25 ML, the yield of surface nitrogen is significantly less, as indicated by the N₂ TPD peak area. Atomic nitrogen readily reacts with hydrogen to produce the NH species, which is characterized with RAIRS by an intense and narrow (FWHM ∼ 4 cm⁻¹) peak at 3322 cm⁻¹. The areas of the H₂ TPD peak associated with NH dissociation and the XPS N 1s peak associated with the NH species indicate that not all of the surface N atoms can be converted to NH by the methods used here.     

Photon-induced chemical vapor deposition of molybdenum on Pt(1 1 1)

Temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) have been employed to study the adsorption and photon-induced decomposition of Mo(CO)₆. Mo(CO)₆ adsorbs molecularly on a Pt(1 1 1) surface with weak interaction at 100 K and desorbs intact at 210 K without undergoing thermal decomposition. Adsorbed Mo(CO)₆ undergoes decarbonylation to form surface Mo(CO)_x (x ? 5) under irradiation of ultraviolet light. The Mo(CO)_x species can release further CO ligands to form Mo adatoms with CO desorption at 285 K. In addition, a fraction of the released CO ligands transfers onto the Pt surface and subsequently desorbs at 350-550 K. The resulting Mo layer deposited on the Pt surface is nearly free of contamination by C and O. The deposited Mo adatoms can diffuse into the bulk Pt at temperatures above 1070 K.