This thesis deals with the influence of the structure andchemical composition of platinum surfaces on the adsorption ofsome molecules. Three main lines can be distinguished : 1) thecharacterisation of clean/modified surfaces, 2) the adsorptionof some simple atoms and molecules on these surfaces andfinally 3) the adsorption of 2-butenal, a bi-functionalmolecule containing a C=C group conjugated with a C=O group.The main tools used in this work are scanning tunnellingmicroscopy, photoelectron spectroscopy and high-resolutionelectron energy loss spectroscopy, in combination with quantumchemical calculations. The platinum (111)(1× 1) and (110)(1× 2) surfacesare chosen as substrates. Pt(111) is a non-reconstructedclose-packed surface, while the Pt(110) surface is open, due toits missing row (MR) reconstruction, which results in thealternation of ridges, {111} microfacets and valleys. Titaniumgrows on Pt(111) in a Volmer-Weber mode. Pronounced reactionsbetween Pt and Ti are detected already at room temperature asthe Ti2p and Pt4f7/2core-level shifts are characteristic of the Pt3Ti alloy. Carbon segregated on the (110) surfaceappears as extended graphitic regions, which smoothen thesubstrate. Sn deposition at room temperature on Pt(110) resultsin the appearance of small islands, randomly spread over thesurface. The presence of mobile Sn ad-atoms and Pt-Sn-Ptalloyed chains in the valley of the MR reconstruction is alsoevidenced. Annealing the surface results in the rearrangementof the tin in the surface layer, together with a globalshortening of the terraces in the [110]direction and anincreased density of (1× n) (n&gt;2) defects. The adsorption of atomic hydrogen and oxygen has beenperformed on the Pt(111)( √ 3x √3)R30º surfacealloy and on Pt(110)(1× 2) respectively. The adsorptionsite of these atoms is changed as compared to the onedetermined on the clean Pt(111) surface (i.e. fcc hollow site): H is adsorbed on-top site on the (√3× √3)surface alloy, and O sits on the ridge of the missing rowreconstruction in bridge site. Carbon monoxide adsorption wasperformed on Pt(111) and Pt(110)(1× 2) surfaces, modifiedor not by tin. On the unmodified (111) surface, CO adsorbsfirst in top site, thenin bridge. Changing the geometry of thesurface to the (110) results in the vanishing of the bridgesite population. Modifying these surfaces by Sn does not changethe CO adsorption site. Finally, 2-butenal (CH3-CH=CH-CH=O) has been adsorbed at 100 K on thePt(111) surface and the Sn/Pt(111) surface alloys. On theunmodified Pt surface, comparison with results obtained forpropene (CH2=CH-CH3) adsorption evidences the involvement of the C=Cgroup of the 2-butenal molecule in the bonding to the Ptsurface. The carbonyl group is also suggested to take part inthe bonding, through a σccη1(O) configuration. This carbonyl group bondingdisappears when Sn is alloyed to the surface, and the formationof a new physisorbed phase is detected. / <p>NR 20140805</p>

<p>This thesis deals with the influence of the structure andchemical composition of platinum surfaces on the adsorption ofsome molecules. Three main lines can be distinguished : 1) thecharacterisation of clean/modified surfaces, 2) the adsorptionof some simple atoms and molecules on these surfaces andfinally 3) the adsorption of 2-butenal, a bi-functionalmolecule containing a C=C group conjugated with a C=O group.The main tools used in this work are scanning tunnellingmicroscopy, photoelectron spectroscopy and high-resolutionelectron energy loss spectroscopy, in combination with quantumchemical calculations.</p><p>The platinum (111)(1× 1) and (110)(1× 2) surfacesare chosen as substrates. Pt(111) is a non-reconstructedclose-packed surface, while the Pt(110) surface is open, due toits missing row (MR) reconstruction, which results in thealternation of ridges, {111} microfacets and valleys. Titaniumgrows on Pt(111) in a Volmer-Weber mode. Pronounced reactionsbetween Pt and Ti are detected already at room temperature asthe Ti2p and Pt4f_7/2core-level shifts are characteristic of the Pt₃Ti alloy. Carbon segregated on the (110) surfaceappears as extended graphitic regions, which smoothen thesubstrate. Sn deposition at room temperature on Pt(110) resultsin the appearance of small islands, randomly spread over thesurface. The presence of mobile Sn ad-atoms and Pt-Sn-Ptalloyed chains in the valley of the MR reconstruction is alsoevidenced. Annealing the surface results in the rearrangementof the tin in the surface layer, together with a globalshortening of the terraces in the [110]direction and anincreased density of (1× n) (n>2) defects.</p><p>The adsorption of atomic hydrogen and oxygen has beenperformed on the Pt(111)( √ 3x √3)R30º surfacealloy and on Pt(110)(1× 2) respectively. The adsorptionsite of these atoms is changed as compared to the onedetermined on the clean Pt(111) surface (i.e. fcc hollow site): H is adsorbed on-top site on the (√3× √3)surface alloy, and O sits on the ridge of the missing rowreconstruction in bridge site. Carbon monoxide adsorption wasperformed on Pt(111) and Pt(110)(1× 2) surfaces, modifiedor not by tin. On the unmodified (111) surface, CO adsorbsfirst in top site, thenin bridge. Changing the geometry of thesurface to the (110) results in the vanishing of the bridgesite population. Modifying these surfaces by Sn does not changethe CO adsorption site.</p><p>Finally, 2-butenal (CH₃-CH=CH-CH=O) has been adsorbed at 100 K on thePt(111) surface and the Sn/Pt(111) surface alloys. On theunmodified Pt surface, comparison with results obtained forpropene (CH₂=CH-CH₃) adsorption evidences the involvement of the C=Cgroup of the 2-butenal molecule in the bonding to the Ptsurface. The carbonyl group is also suggested to take part inthe bonding, through a σ_ccη₁(O) configuration. This carbonyl group bondingdisappears when Sn is alloyed to the surface, and the formationof a new physisorbed phase is detected.</p>

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Abstract In this thesis oxidation of a pure and alloyed Cu surface was studied using density functional theory based calculations. The mechanism and energetics behind experimentally observed missing row reconstruction on a pure Cu(100) surface were studied. Examination of the formation of the missing row was approached by studying the profitableness of vacancy formation to the surface at oxygen coverages below and equal to 0.5 ML. However, an ideal surface was in all cases more favourable in energy than vacancy included structures. Therefore an additional Cu atom was added to the simulation cell to promote vacancy formation. A consequence of this on-surface Cu addition was the identifying of a new energetically favoured Cu-O-Cu chain formation. This newly identified structure is a possible transition state in the path from an ideal surface to a reconstructed one. Copper(I)oxide formation through sub-surface adsorption was examined on a reconstructed Cu(100) surface. At low O coverage on-surface adsorption was found to be much more favoured than adsorption on sub-surface sites. However, when coverage increased to 0.75 ML structures with both on-surface and sub-surface adsorbates possessed the lowest energy. Furthermore, the diffusion barriers to the sub-surface adsorption sites were low. Both these facts support the conclusion that the transition from the reconstructed missing row structure to the copper(I)oxide takes place without any large energy effort. The adsorption induced segregation of copper on a Ag/Cu(100) surface was studied by calculating the surface energies of slabs where the silver layer was positioned at different depths with varying O coverage. In addition, the segregation energies were also calculated with two Ag compositions. It was discovered that without oxygen adsorbates silver atoms lying on top of the surface were favoured but the surface segregation probability of Cu increases with increasing O coverage. The same calculation procedure was expanded to study the segregation probability of five additional alloy metals with a Cu surface. Without oxygen present Mg, Al and Zn possess a weak tendency to segregate to the surface, however, V and Cr prefer to stay in the bulk. The addition of oxygen adsorbates on the surface causes the segregation of all the dopants to the top of the surface. With the Al dopant the effect of the surface orientation and the oxygen coverage were also studied. The bonds between adsorbates and the surface were strongest with the densest surface, (111), and weakest with the most opened surface, (110). Furthermore, the enrichment probability was largest in the case of the (111) surface and lowest with the (110) surface. Probability increased with increasing oxygen coverage. / Tiivistelmä Tässä väitöstyössä on tutkittu puhtaan ja seostetun kuparipinnan hapettumista tiheysfunktionaaliteoriaan perustuvilla laskuilla. Kokeellisesti Cu(100) pinnan on havaittu rekonstruoituvan hapen vaikutuksesta. Rekonstruoitumisen aikana ideaalisesta pinnasta irtoaa joka neljäs pintakuparirivi ja muodostuu niin kutsuttu missing row- rakenne. Tämän rakenteen muodostumismekanismia ja muodostumiseen kuluvaa energiaa tutkittiin vertaamalla pintavakansillisten rakenteiden pintaenergioita vastaaviin ideaalipinnan arvoihin vaihtelevalla happipeitolla. Koska ideaalipinta oli kaikilla peittoasteilla energeettisesti suotuisampi kuin vakanssirakenne, yksittäisiä kupariatomeja lisättiin pinnalle stabiloimaan vakanssirakenteita. Kuparilisäyksen seurauksena löydettiin uusi energeettisesti edullinen Cu-O-Cu ketjurakenne. Tämä rakenne on mahdollinen ideaalisen ja rekonstruoituneen pinnan välinen siirtymätila. Kupari(I)oksidin muodostumista pinnanalaisen happiadsorption kautta tutkittiin rekonstruoituneella Cu(100) pinnalla. Pienillä happi-peittoasteilla pinnanpäällisen adsorption havaittiin olevan huomattavasti suotuisampaa kuin pinnanalaisen adsorption. Kuitenkin happi peiton kasvaessa 0,75 ML:iin rakenteet, joissa oli adsorbaatteja sekä pinnan alla että päällä, tulivat muita suotuisimmiksi. Myös lasketut energiavallit hapen diffuusiolle pinnalta pinnan alle olivat hyvin pieniä. Kaikki tulokset viittaavat siihen, että rekonstruoitunut Cu(100) pinta hapettuu helposti kupari(I)oksidiksi. Happiadsorption aikaansaamaa kuparin rikastumista (segregaatio) hopeakupariseosmetallin pinnalle tutkittiin laskemalla vaihtelevilla happipeitoilla pintaenergiat kuparipinnoille, joissa ensimmäinen, toinen ja kolmas kuparikerros oli korvattu hopealla. Myös segregaatioenergiat laskettiin kahdella eri seoskoostumuksella. Saatujen tulosten mukaan ilman happiadsoptiota hopea segregoituu pinnalle, kun taas hapen peittoasteen kasvaessa kupari rikastuu pinnalle. Samaa tutkimustapaa käytettiin myös tarkasteltaessa viiden muun seosmetallin segregaatiotodennäköisyyttä kuparipinnalla. Ilman pintahappea magnesiumilla, alumiinilla ja sinkillä oli heikko taipumus rikastua pinnalle, kun taas vanadium ja kromi pysyivät syvemmällä metallissa. Sen sijaan happea lisättäessä kaikki tutkitut seosmetallit pyrkivät siirtymään kohti pintaa. Myös hapen peiton sekä pintaorientaation vaikutusta segregaatioon tutkittiin hopeakuparipinnalla. Sekä happiadsorbaattien ja pinnan välinen sidos että segregaatiotodennäköisyys oli sitä voimakkaampaa, mitä tiheämmästä pinnasta oli kyse. Segregaatiotodennäköisyys kasvoi pinta-adsorption lisääntyessä.