Growth and sintering of Pd clusters on alpha-Al2O3(0001)

The growth and sintering of Pd nanoparticles on alpha-Al(2)O(3)(0001) have been studied by noncontact atomic force microscopy (NC-AFM), low-energy ion scattering spectroscopy (LEIS), temperature-programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS). This is the first study of metal nanoparticles on a well-defined oxide surface where both NC-AFM and LEIS are used for characterization. These prove to be a powerful combination in assessing particle dimensions. The clean alumina surface showed atomically flat, 200-700 nm wide terraces. The sharp step edges are straight (within our resolution) for lengths of >300 nm and have heights in multiples of 0.2 nm. The Pd grows initially as two-dimensional (2D) islands at 300 K, with the transition to 3D particle growth at 0.25 ML (ML=monolayers). Upon heating at 1 K/s, the Pd starts to sinter below 400 K, and sinters at a nearly constant rate with increasing temperature, covering approximately 50% less of the alumina surface by approximately 1000 K, with a doubling in particle diameter and an eightfold decrease in particle number density. By approximately 1000 K, the number density was approximately 9 x 10(11)cm(2) for 0.8 ML of Pd, with an average diameter of 5 nm and an average thickness of 1 nm.     

Interaction of SO3 with c-ZrO2(111) films on Pt(111)

Single-crystalline sulfated c-ZrO2(111) films of the cubic (c) type have been prepared by reactive deposition of Zr onto Pt(111) in an O2 atmosphere and subsequent exposition to a SO3 atmosphere. The morphology, atomic structure, and composition have been examined by scanning tunneling microscopy, low-energy electron diffraction (LEED), Auger electron spectroscopy, and density functional theory (DFT) calculations. The clean c-ZrO2(111) films display a (2x2) surface structure. During SO3 exposure at room temperature, a clear (radical3xradical3)R30 degrees structure develops. At about 700 K, the SO3-induced (radical3xradical3)R30 degrees structure disappears and the bright (2x2) LEED pattern of the clean ZrO2 films reappears. The energies of plausible c-ZrO2(111)/SO3 structures have been examined by DFT. The (radical3xradical3)R30 degrees structure found in the experiments turned out to be the most stable one for temperatures below 700 K. At temperatures around 700 K, a disordered low coverage structure may exist, which can not be observed by conventional LEED. A comparison of cubic zirconia surfaces with the alternative tetragonal system yields similar results for the SO3 adsorption in the DFT calculations and shows that c-ZrO2 surfaces are good models for the industrial used tetragonal ZrO2 supports.     

Epitaxial BaTiO3(100) films on Pt(100): a low-energy electron diffraction, scanning tunneling microscopy, and x-ray photoelectron spectroscopy study

The growth of epitaxial ultrathin BaTiO(3) films on a Pt(100) substrate has been studied by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and x-ray photoelectron spectroscopy (XPS). The films have been prepared by radio-frequency-assisted magnetron sputter deposition at room temperature and develop a long-range order upon annealing at 900 K in O(2). By adjusting the Ar and O(2) partial pressures of the sputter gas, the stoichiometry was tuned to match that of a BaTiO(3)(100) single crystal as determined by XPS. STM reveals the growth of continuous BaTiO(3) films with unit cell high islands on top. With LEED already for monolayer thicknesses, the formation of a BaTiO(3)(100)-(1 × 1) structure has been observed. Films of 2-3 unit cell thickness show a brilliant (1 × 1) LEED pattern for which an extended set of LEED I-V data has been acquired. At temperatures above 1050 K the BaTiO(3) thin film starts to decay by formation of vacancy islands. In addition (4 × 4) and (3 × 3) surface reconstructions develop upon prolonged heating.     

Interaction of water with ordered theta-Al(2)O(3) ultrathin films grown on NiAl(100)

The structure of an ordered, ultrathin theta-Al(2)O(3) film grown on a NiAl(100) single-crystal surface was studied by Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and low-energy electron diffraction (LEED), and its interaction with water was investigated with temperature programmed desorption (TPD) and XPS. Our results indicate that H(2)O adsorption on the theta-Al(2)O(3)/NiAl(100) surface is predominantly molecular rather than dissociative. For theta(H)()2(O) < 1 ML (ML = monolayer), H(2)O molecules were found to populate Al(3+) cation sites to form isolated H(2)O species aligned in a row along the cation sites on the oxide surface with a repulsive interaction between them. For theta(H)()2(O) > 1 ML, three-dimensional ice multilayers were observed to form, which then desorb during TPD with approximate zero-order kinetics as expected. A small extent of H(2)O dissociation was observed to occur on the theta-Al(2)O(3)/NiAl(100) surface, which was attributed to the presence of a low concentration of oxygen atom vacancies. Titration of these defect sites with adsorbed H(2)O molecules revealed an estimated defect density of 0.05 ML for the theta-Al(2)O(3)/NiAl(100) system consistent with the ordered nature of the synthesized oxide film.     

Growth and electronic structure of Sm on thin Al2O3/Ni3Al(111) films

The growth and electronic structure of vapor-deposited Sm on a well-ordered Al(2)O(3)/Ni(3)Al(111) ultrathin film under ultrahigh vacuum conditions at room temperature have been studied comprehensively using synchrotron radiation photoemission spectroscopy, X-ray photoelectron spectroscopy, work function measurements, scanning tunneling microscopy, and low-energy electron diffraction. Our results indicate that at room temperature Sm grows in a layer-by-layer fashion up to at least 1 ML, followed by three-dimensional growth. The interaction of Sm with Al(2)O(3) thin films leads to an initial oxidation of Sm, accompanied by a parallel reduction of the Al(2)O(3) substrate. Both the oxidation states of Sm(2+) and Sm(3+) are found at low coverage (<1 ML). The concentration of Sm(2+) saturates below 0.4 ML, while that of Sm(3+) keeps increasing until the metallic state of Sm appears at high coverages.     

Ultrathin chromium oxide films on the W(100) surface

Ultrathin chromium oxide films were prepared on a W(100) surface under ultrahigh-vacuum conditions and investigated in situ by X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and low-energy electron diffraction. The results show that, at Cr coverage of less than 1 monolayer, CrO2 is formed by oxidizing pre-deposited Cr at 300-320 K in approximately 10(-7) mbar oxygen. However, an increase of temperature causes formation of Cr2O3. At Cr coverage above 1 monolayer, only Cr2O3 is detected.     

Initial oxidation and interfacial diffusion of Zn on faceted MgO(111) films

The interaction of zinc and faceted MgO(111) thin films prepared on a Mo(110) substrate was investigated in situ by using various surface analysis techniques, including X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, Auger electron spectroscopy, high-resolution electron energy loss spectroscopy, and low-energy electron diffraction. The results revealed that three-dimensional Zn islands exist on the faceted MgO(111) films and that no chemical interaction takes place at the interface at room temperature. Initially, deposited Zn is stable at temperatures below 400 K and diffuses into MgO at temperatures above 425 K. A portion of Zn is oxidized at approximately 10 (-6) mbar O 2 at room temperature. An interfacial phase of Zn x Mg 1- x O was formed after Zn was exposed to approximately 10 (-6) mbar O 2 at temperatures >or=500 K. The faceted structure on the MgO(111) surface is of a disadvantage for the epitaxial growth of ZnO films.     

Pressure-dependent Ni-O phase transitions and Ni oxide formation on Pt(111): an in situ STM study at elevated temperatures

Growth, atomic structure and O2 partial pressure dependent phase transitions of Ni-O structures and thin NiO films on Pt(111) have been studied using scanning tunnelling microscopy (STM), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES). In situ STM experiments were performed during film growth by reactive metal deposition at elevated temperatures (400-550 K) and variable O2 pressure. Depending on the substrate temperature, one-dimensional network-like Ni-O structures and islands with (7x1) and (4x2) reconstructions are formed during the initial stages of growth. These structures transform reversibly to a (2x2) reconstruction in a narrow O2 pressure range of 1.5-2x10(-6) mbar and can be monitored by in situ STM. Upon reduction of the O2 pressure to <10(-10) mbar pseudomorphic Ni monolayers are obtained. The defect-free ordering of Ni atoms on Pt(111) in a single stacking domain indicates an O-surfactant induced growth mode. The structural properties of the O2 pressure-dependent Ni-O phases are discussed in a simple model assuming NiO(001)-like atomic arrangements in the adsorbate overlayer. At higher coverage stable (111)-oriented NiO islands grow in a three-dimensional mode.     

Surface chemistry on bimetallic alloy surfaces: adsorption of anions and oxidation of CO on Pt3Sn(111)

The microscopic structure of the Pt(3)Sn(111) surface in an electrochemical environment has been studied by a combination of ex situ low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and low-energy ion scattering (LEIS) and in situ surface X-ray scattering (SXS) and Fourier transform infrared (FTIR) spectroscopy. In ultrahigh vacuum (UHV) the clean-annealed surface produces a p(2 x 2) LEED pattern consistent with the surface composition, determined by LEIS, of 25 at. % Sn. SXS results show that the p(2 x 2) structure can be "transferred" from UHV into 0.5 M H(2)SO(4) and that the surface structure remains stable from 0.05 to 0.8 V. At 0.05 V the expansion of Pt surface atoms, ca. +2% from the bulk lattice spacing, is induced by adsorption of underpotential-deposited (UPD) hydrogen. At 0.5 V, where Pt atoms are covered by (bi)sulfate anions, the topmost layer is contracted relative to 0.05 V, although Sn atoms expand significantly, ca. 8.5%. The p(2 x 2) structure is stable even in solutions containing CO. In contrast to the Pt(111)-CO system, no ordered structures of CO are formed on the Pt(3)Sn(111) surface and the topmost layer expands relatively little (ca. 1.5%) from the bulk lattice spacing upon the adsorption of CO. The binding site geometry of CO on Pt(3)Sn(111) is determined by FTIR. In contrast to the near invariant band shape of a-top CO on Pt(111), changes in band morphology (splitting of the band) and vibrational properties (increase in the frequency mode) are clearly visible on the Pt(3)Sn(111) surface. To explain the line shape of the CO bands, we suggest that in addition to alloying effects other factors, such as intermolecular repulsion between coadsorbed CO and OH species, are controlling segregation of CO into cluster domains where the local CO coverage is different from the coverage expected for the CO-CO interaction on an unmodified Pt(111) surface.     

Ba deposition and oxidation on theta-Al2O3/NiAl(100) ultrathin films. Part II: O2(g) assisted Ba oxidation

Ba deposition on a theta-Al(2)O(3)/NiAl(100) substrate and its oxidation with gas-phase O(2) at various surface temperatures are investigated using X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and temperature programmed desorption (TPD) techniques. Oxidation of metallic Ba by gas-phase O(2) at 800 K results in the growth of 2D and 3D BaO surface domains. Saturation of a metallic Ba layer deposited on theta-Al(2)O(3)/NiAl(100) with O(2)(g) at 300 K reveals the formation of BaO(2)-like surface states. These metastable peroxide (O(2)(2-)) states are converted to regular oxide (O(2-)) states at higher temperatures (800 K). In terms of thermal stability, BaO surface layers (theta(Ba) < 5 ML) that are formed by O(2)(g) assisted oxidation on the theta-Al(2)O(3)/NiAl(100) substrate are significantly more stable (with a desorption/decomposition temperature of c.a. 1050 K) than the thick (2 < theta(Ba) < 10 ML) metallic/partially oxidized Ba layers prepared in the absence of gas-phase O(2), whose multilayer desorption features appear as low as 700 K.     

Structural evolution of perfluoro-pentacene films on Ag(111): transition from 2D to 3D growth

The structural evolution and thermal stability of perfluoro-pentacene (PF-PEN) thin films on Ag(111) have been studied by means of low-temperature scanning tunnelling microscopy (STM), low-energy electron diffraction (LEED), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and thermal desorption spectroscopy (TDS). Well-defined monolayer films can be prepared by utilizing the different adsorption energy of mono- and multilayer films and selectively desorbing multilayers upon careful heating at 380 K, whereas at temperatures above 400 K, a dissociation occurs. In the first monolayer, the molecules adopt a planar adsorption geometry and form a well-ordered commensurate (6 × 3) superstructure where molecules are uniformly oriented with their long axis along the <110> azimuth. This molecular orientation is also maintained in the second layer, where molecules exhibit a staggered packing motif, whereas further deposition leads to the formation of isolated, tall islands. Moreover, on smooth silver surfaces with extended terraces, growth of PF-PEN onto beforehand prepared long-range ordered monolayer films at elevated temperature leads to needle-like islands that are uniformly aligned at substrate steps along <110> azimuth directions.     

Surface and subsurface oxidation of Mo2C/Mo(100): low-energy ion-scattering, auger electron, angle-resolved X-ray photoelectron, and mass spectroscopy studies

The interaction of oxygen with a carburized Mo(100) surface was investigated at different temperatures (300-1000 K). The different information depths of low-energy ion-scattering (LEIS) spectroscopy, with topmost layer sensitivity, Auger electron spectroscopy (AES), and angle-resolved X-ray photoelectron spectroscopy (ARXPS) allowed us to discriminate between reactions on the topmost layer and subsurface transformations. According to ARXPS measurements, a carbide overlayer was prepared by the high-temperature decomposition of C(2)H(4) on Mo(100), and the carbon distribution proved to be homogeneous with a Mo(2)C stoichiometry down to the information depth of XPS. O(2) adsorbs dissociatively on the carbide layer at room temperature. One part of the chemisorbed oxygen is bound to both C and Mo sites, indicated by LEIS. Another fraction of oxygen atoms probably resides in the hollow sites not occupied by C. The removal of C from the outermost layer by O(2), in the form of CO, detected by mass spectroscopy (MS), was observed at 500-600 K. The carbon-depleted first layer is able to adsorb more oxygen compared to the Mo(2)C/Mo(100) surface. Applying higher doses of O(2) at 800 K results in the inward diffusion of O and the partial oxidation of Mo atoms. This process, however, is not accompanied by the removal of C from subsurface sites. The depletion of C from the bulk starts only at 900 K (as shown by MS, AES, and XPS), very probably by the diffusion of C to the surface followed by its reaction with oxygen. At T(ads) = 1000 K, the carbon content of the sample, down to the information depth of XPS, decreased further, accompanied by the attenuation of the C concentration gradient and a substantially decreased amount of oxygen.     

Ultrathin metals films on W(221): Structure, electronic properties and reactivity

Nanoscale pyramidal facets with (211) faces are formed when W(111) surface is covered by monolayer film of certain metals (including Pt, Pd and Au) and annealed to T ≥ 750 K. In the present work, we focus on the structure, electronic properties and reactivity of planar W(211) covered by ultrathin films of platinum and palladium. The measurements include soft X-ray photoelectron spectroscopy using synchrotron radiation, Auger electron spectroscopy, low energy electron diffraction (LEED) and thermal desorption spectroscopy. The metal film growth and evolution during annealing has been investigated for coverages ranging from 0 to 8 monolayers. The films grow initially in a layer-by-layer mode at 300 K. LEED, Auger, and Surface Core Level Shift (SCLS) measurements reveal that for coverages of one monolayer, the films are stable up to temperatures at which desorption occurs. In contrast, at higher coverages, SCLS data indicate that surface alloys are formed upon annealing films of Pt and Pd; surface alloy formation is not seen for Au overlayers. These findings are discussed in terms of structural and electronic properties of these bimetallic systems. Relevance to catalytic properties for acetylene cyclization over Pd/W(211) is also discussed.     

The growth of silver on an ordered alumina surface

The growth of Ag on an ordered Al2O3 surface was studied by low energy ion scattering spectroscopy (LEIS), scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and temperature programmed desorption (TPD). Three-dimensional (3D) growth of Ag clusters was observed with STM and LEIS, with the cluster size increasing with Ag coverage. The XPS core level binding energies and the Auger parameters indicate a weak interaction between the Ag clusters and the Al2O3 support. Final state effects are determined to be the primary contribution to the Ag core level binding energy shift. Nonzero order kinetics was observed for Ag desorption in TPD with the Ag sublimation energy decreasing with decreasing cluster size.     

Electronic properties of Cu clusters and islands and their reaction with O2 on SnO2(110) surfaces

The deposition of Cu on SnO₂(110) surfaces, and its oxidation to Cu_xO, have been studied by low-energy electron diffraction (LEED) and angle-integrated photoemission using synchrotron radiation photoemission spectroscopy (SRPES). With the growth of copper on SnO₂(110), which was found to follow the Volmer-Weber (“islanding”) growth mode, a small amount of metal-phase Sn segregates to the surface, and even when the copper thickness reaches several tens of Å, Sn metal still is seen at the surface. But when this surface is annealed at 800 K in 5 × 10^?6 mbar O₂ for 20 min, the Sn atoms are totally converted to SnO₂. Simultaneously, the deposited Cu atoms become oxidized. The surface charges up both during LEED and SRPES data acquisition. The clean SnO₂(110) surface shows a 1 × 1 structure. With Cu deposition, the substrate LEED pattern gradually becomes weaker. With even more copper deposited, a Cu(111)-1 × 1-oriented particle structure appears, indicating coalescence of the Cu islands to 3-dimensional Cu(111) epitaxy. After subsequent heating to 500 K, the substrate signal appears again, and we see the SnO₂ 1 × 1 pattern. In conclusion, Cu atoms quite easily form clusters on the SnO₂(110) surface already after a slight heat treatment. The results show that this system is quite active towards O₂ gas exposure, and that the surface conductivity changes during O₂ exposure.     

清洁及部分氧化的Ni_3Ti(0001)表面CO吸附的HREELS研究

用离子散射谱（ＩＳＳ）、俄歇电子能谱（ＡＥＳ）及低能电子衍射（ＬＥＥＤ）技术对Ｎｉ３Ｔｉ（０００１）表面结构与组成进行考察后，主要采用高分辨电子能量损失谱（ＨＲＥＥＬＳ），以ＣＯ为探针分子，研究了清洁及部分氧化的Ｎｉ３Ｔｉ（０００１）表面上Ｎｉ，Ｔｉ间的相互作用及对ＣＯ吸附态的影响．结果表明：（１）在最表层几乎完全为Ｎｉ的Ｎｉ３Ｔｉ（０００１）清洁规整表面上，ＣＯ没有发生解离；（２）次表层Ｔｉ原子与最表层Ｎｉ原子间的电子相互作用，使初始吸附的ＣＯ伸缩振动与Ｎｉ（１１１）相比向低频位移约６０ｃｍ－１；（３）适量ＣＯ暴露后，ＣＯ氧端与近邻Ｔｉ原子的成键作用产生了一种新的Ｎｉｘ－Ｃ－Ｏ－Ｔｉｙ物种．Ｎｉ３Ｔｉ（０００１）表面部分氧化后，上述（２）和（３）作用消失     

Adsorption of bromobenzene on periodically stepped and nonstepped NiO(100)

Periodically stepped NiO(100) surfaces were prepared and characterized with low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD). Two vicinal NiO(100) single-crystal samples were cut, oriented, and polished with regular, repeating monatomic steps in six-atom or seven-atom terrace widths. LEED diffraction patterns showed characteristic spot-splitting that corresponded to the appropriate terrace and step height. The nonstepped and stepped NiO(100) surfaces were exposed to bromobenzene at 130 K first to produce a molecularly adsorbed monolayer species and then, with increased exposure, a multilayer adsorbate. An additional adsorbate species, observed only on the stepped surfaces, was found to desorb at 145 K by two competing pathways. One pathway, which saturates at low coverages, leaves bromine behind on the substrate and results in dehalogenation. The other pathway yields molecular desorption at 145 K, but is only observed in detectable amounts after the dehalogenation pathway is saturated. On both stepped and nonstepped NiO(100) substrates, adsorbed bromine resulting from dehalogenation processes appears as nickel bromide, determined by the Br 3p XPS data.     

Interactions of O(2) with Pd nanoparticles on alpha-Al(2)O(3)(0001) at low and high O(2) pressures

The interaction of O(2) with small Pd particles (2-10 nm) supported on an alpha-Al(2)O(3)(0001) single crystal under both ultrahigh vacuum (UHV) and high-pressure conditions has been studied by temperature-programmed desorption (TPD), temperature-programmed low-energy ion scattering (TP-LEIS), and X-ray photoelectron spectroscopy (XPS). A low O(2) exposure (30 L) at 500 K leads to surface oxygen adatoms on the Pd nanoparticles, which desorb in TPD as O(2) in a peak at approximately 880 K. Surface O adatoms on the smallest Pd particles move to subsurface sites starting at 400 K, and they almost all move subsurface by approximately 750 K, desorbing mainly at considerably higher temperature. The dominant oxygen species above 700 K is subsurface, implying that it is more stable than oxygen adatoms on Pd. Exposures of the Pd nanoparticles to 25 Torr O(2) at 373-473 K readily convert the Pd to a species whose Pd XPS peak shifts by the same amount as the binding energy difference between bulk Pd and bulk PdO. We attribute this to PdO nanoparticles (or a thin film of PdO on or under the Pd for the larger particles). The decomposition of the PdO on these nanoparticles to Pd in an equilibrium O(2) pressure of 10-7 Torr does not occur until approximately 750 K, or approximately 200 K higher than the equilibrium decomposition of bulk PdO. This is attributed to the higher energy of Pd nanoparticles compared to bulk Pd and, for the larger particles, to the adhesion energy of the PdO film to the Pd, both of which stabilize the PdO on these Pd nanoparticles relative to bulk PdO. This PdO-like film on the larger particles may be similar to the ordered oxide thin film previously reported to form on Pd(111) but may also reside at the alpha-Al(2)O(3) interface and be partially stabilized by adhesion to this interface.     

Reactivity of V2O3(0001) surfaces: molecular vs dissociative adsorption of water

The adsorption of water on V2O3(0001) surfaces has been investigated by thermal desorption spectroscopy, high-resolution electron energy loss spectroscopy, and X-ray photoelectron spectroscopy with use of synchrotron radiation. The V2O3(0001) surfaces have been generated in epitaxial thin film form on a Rh(111) substrate with three different surface terminations according to the particular preparation conditions. The stable surface in thermodynamic equilibrium with the bulk is formed by a vanadyl (VO) (1x1) surface layer, but an oxygen-rich (radical3xradical3)R30 degrees reconstruction can be prepared under a higher chemical potential of oxygen (microO), whereas a V-terminated surface consisting of a vanadium surface layer requires a low microO, which can be achieved experimentally by the deposition of V atoms onto the (1x1) VO surface. The latter two surfaces have been used to model, in a controlled way, oxygen and vanadium containing defect centres on V2O3. On the (1x1) V=O and (radical3xradical3)R30 degrees surfaces, which expose only oxygen surface sites, the experimental results indicate consistently that the molecular adsorption of water provides the predominant adsorption channel. In contrast, on the V-terminated (1/radical3x1/radical3)R30 degrees surface the dissociation of water and the formation of surface hydroxyl species at 100 K is readily observed. Besides the dissociative adsorption a molecular adsorption channel exists also on the V-terminated V2O3(0001) surface, so that the water monolayer consists of both OH and molecular H2O species. The V surface layer on V2O3 is very reactive and is reoxidised by adsorbed water at 250 K, yielding surface vanadyl species. The results of this study indicate that V surface centres are necessary for the dissociation of water on V2O3 surfaces.     

Preparation and characterisation of hydroxide stabilised ZnO(0001)-Zn-OH surfaces

Two different approaches under ambient conditions were developed for the preparation of clean, non-reconstructed, single crystalline ZnO(0001)-Zn surfaces. The surface preparation by a wet chemical etching procedure was compared with the same treatment in combination with a subsequent heat treatment in humidified oxygen atmosphere. Depending on the preparation technique, atomically flat terraces with a width of 100 nm to several micrometers were observed using an atomic force microscope (AFM). The obtained surface structures were further characterized by means of angle resolved X-ray photoelectron spectroscopy (AR-XPS), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED) measurements. Based on these results it is shown that the obtained surfaces are, in contrast to surfaces prepared under UHV conditions, stabilised by the adsorption of a monolayer of hydroxides. The important role of H(2)O during the heat treatment is pointed out by comparing the results of the same heat treatment in the absence of water. H(2)O turned out to play an important role in the reorganization process of the surface at elevated temperatures, thereby yielding extremely large atomically flat terraces. The terminating edges of these terraces were found to include 120 degrees and 60 degrees angles, thus perfectly reflecting the hexagonal surface structure.