Electronic and structural study of Pt-modified Au vicinal surfaces: a model system for Pt–Au catalysts

FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOTwo single crystalline surfaces of Au vicinal to the (111) plane were modified with Pt and studied using scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS) in ultra-high vacuum environment. The vicinal surfaces studied are Au(332) and Au(887) and different Pt coverage (θPt) were deposited on each surface. From STM images we determine that Pt deposits on both surfaces as nanoislands with heights ranging from 1 ML to 3 ML depending on θPt. On both surfaces the early growth of Pt ad-islands occurs at the lower part of the step edge, with Pt ad-atoms being incorporated into the steps in some cases. XPS results indicate that partial alloying of Pt occurs at the interface at room temperature and at all coverage, as suggested by the negative chemical shift of Pt 4f core line, indicating an upward shift of the d-band center of the alloyed Pt. Also, the existence of a segregated Pt phase especially at higher coverage is detected by XPS. Sample annealing indicates that the temperature rise promotes a further incorporation of Pt atoms into the Au substrate as supported by STM and XPS results. Additionally, the catalytic activity of different PtAu systems reported in the literature for some electrochemical reactions is discussed considering our findings. © 2014 The Owner Societies.Two single crystalline surfaces of Au vicinal to the (111) plane were modified with Pt and studied using scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS) in ultra-high vacuum environment. The vicinal surfaces studied are Au(332) and Au(887) and different Pt coverage (yPt) were deposited on each surface. From STM images we determine that Pt deposits on both surfaces as nanoislands with heights ranging from 1 ML to 3 ML depending on yPt. On both surfaces the early growth of Pt ad-islands occurs at the lower part of the step edge, with Pt ad-atoms being incorporated into the steps in some cases. XPS results indicate that partial alloying of Pt occurs at the interface at room temperature and at all coverage, as suggested by the negative chemical shift of Pt 4f core line, indicating an upward shift of the d-band center of the alloyed Pt. Also, the existence of a segregated Pt phase especially at higher coverage is detected by XPS. Sample annealing indicates that the temperature rise promotes a further incorporation of Pt atoms into the Au substrate as supported by STM and XPS results. Additionally, the catalytic activity of different PtAu systems reported in the literature for some electrochemical reactions is discussed considering our findings.Two single crystalline surfaces of Au vicinal to the (111) plane were modified with Pt and studied using scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS) in ultra-high vacuum environment. The vicinal surfaces studied are Au(332) and Au(887) and different Pt coverage (yPt) were deposited on each surface. From STM images we determine that Pt deposits on both surfaces as nanoislands with heights ranging from 1 ML to 3 ML depending on yPt. On both surfaces the early growth of Pt ad-islands occurs at the lower part of the step edge, with Pt ad-atoms being incorporated into the steps in some cases. XPS results indicate that partial alloying of Pt occurs at the interface at room temperature and at all coverage, as suggested by the negative chemical shift of Pt 4f core line, indicating an upward shift of the d-band center of the alloyed Pt. Also, the existence of a segregated Pt phase especially at higher coverage is detected by XPS. Sample annealing indicates that the temperature rise promotes a further incorporation of Pt atoms into the Au substrate as supported by STM and XPS results. Additionally, the catalytic activity of different PtAu systems reported in the literature for some electrochemical reactions is discussed considering our findings.16261332913339FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO07/54829-5; 2011/12.566-3; 2012/16860-6160172/2011-0Greeley, J., Stephens, I.E.L., Bondarenko, A.S., Johansson, T.P., Hansen, H.A., Jaramillo, T.F., Rossmeisl, J., Nørskov, J.K., (2009) Nat. Chem., 1, pp. 552-556Wu, G., More, K.L., Johnston, C.M., Zelenay, P., (2011) Science, 332, pp. 443-447Chu, Y.H., Shul, Y.G., (2010) Int. J. Hydrogen Energy, 35, pp. 11261-11270Kowal, A., Li, M., Shao, M., Sasaki, K., Vukmirovic, M.B., Zhang, J., Marinkovic, N.S., Adzic, R.R., (2009) Nat. Mater., 8, pp. 325-330Xu, C.W., Su, Y.Z., Tan, L.L., Liu, Z.L., Zhang, J.H., Chen, S.A., Jiang, S.P., (2009) Electrochim. Acta, 54, pp. 6322-6326Colmati, F., Antolini, E., Gonzalez, E.R., (2008) J. Alloys Compd., 456, pp. 264-270Antolini, E., (2007) J. Power Sources, 170, pp. 1-12Colmati, F., Antolini, E., Gonzalez, E.R., (2006) J. Power Sources, 157, pp. 98-103Stamenkovic, V.R., Mun, B.S., Mayrhofer, K.J.J., Ross, P.N., Markovic, N.M., (2006) J. Am. Chem. Soc., 128, pp. 8813-8819Freund, H.-J., Pacchioni, G., (2008) Chem. Soc. Rev., 37, pp. 2224-2242Kim, Y., Kim, H.J., Kim, Y.S., Choi, S.M., Seo, M.H., Kim, W.B., (2012) J. Phys. Chem. C, 116, pp. 18093-18100Kwon, Y., Birdja, Y., Spanos, I., Rodriguez, P., Koper, M.T.M., (2012) ACS Catal., 2, pp. 759-764Freitas, R.G., Pereira, E.C., (2010) Electrochim. Acta, 55, pp. 7622-7627Colmati, F., Tremiliosi, G., Gonzalez, E.R., Berna, A., Herrero, E., Feliu, J.M., (2009) Phys. Chem. Chem. Phys., 11, pp. 9114-9123Repain, V., Baudot, G., Ellmer, H., Rousset, S., (2002) Europhys. Lett., 58, p. 730Repain, V., Berroir, J.M., Rousset, S., Lecoeur, J., (1999) Europhys. Lett., 47, p. 435Nahas, Y., Repain, V., Chacon, C., Girard, Y., Rousset, S., (2010) Surf. Sci., 604, pp. 829-833Rohart, S., Girard, Y., Nahas, Y., Repain, V., Rodary, G., Tejeda, A., Rousset, S., (2008) Surf. Sci., 602, pp. 28-36Rohart, S., Baudot, G., Repain, V., Girard, Y., Rousset, S., Bulou, H., Goyhenex, C., Proville, L., (2004) Surf. Sci., 559, pp. 47-62Axel, G., (2009) J. Phys.: Condens. Matter, 21, p. 084205Rodriguez, J., (1996) Surf. Sci. Rep., 24, pp. 223-287Eyrich, M., Diemant, T., Hartmann, H., Bansmann, J., Behm, R.J., (2012) J. Phys. Chem. C, 116, pp. 11154-11165Bowker, M., (1995) Chem. Vap. Deposition, 1, p. 90Xu, J.B., Zhao, T.S., Yang, W.W., Shen, S.Y., (2010) Int. J. Hydrogen Energy, 35, pp. 8699-8706Wang, J., Yin, G., Wang, G., Wang, Z., Gao, Y., (2008) Electrochem. Commun., 10, pp. 831-834Horcas, I., Fernandez, R., Gomez-Rodriguez, J.M., Colchero, J., Gomez-Herrero, J., Baro, A.M., (2007) Rev. Sci. Instrum., 78, pp. 013705-013708Doniach, S., Sunjic, M., (1970) J. Phys. C: Solid State Phys., 3, p. 285Hörnström, S.E., Johansson, L., Flodström, A., Nyholm, R., Schmidt-May, J., (1985) Surf. Sci., 160, pp. 561-570Shevchik, N.J., (1974) Phys. Rev. Lett., 33, p. 1336Powell, C.J., (2012) J. Electron Spectrosc. Relat. Phenom., 185, pp. 1-3Rousset, S., Repain, V., Baudot, G., Garreau, Y., Lecoeur, J., (2003) J. Phys.: Condens. Matter, 15, p. 3363Prévot, G., Girard, Y., Repain, V., Rousset, S., Coati, A., Garreau, Y., Paul, J., Narasimhan, S., (2010) Phys. Rev. B: Condens. Matter Mater. Phys., 81, p. 075415Repain, V., Rohart, S., Girard, Y., Tejeda, A., Rousset, S., (2006) J. Phys.: Condens. Matter, 18, p. 17Repain, V., Baudot, G., Ellmer, H., Rousset, S., (2002) Mater. Sci. Eng., B, 96, pp. 178-187Repain, V., Berroir, J.M., Rousset, S., Lecoeur, J., (2000) Surf. Sci., 447, pp. 152-L156Campiglio, P., Repain, V., Chacon, C., Fruchart, O., Lagoute, J., Girard, Y., Rousset, S., (2011) Surf. Sci., 605, pp. 1165-1169Prieto, M.J., Carbonio, E.A., Landers, R., De Siervo, A., (2013) Surf. Sci., 617, pp. 87-93Antczak, G., Ehrlich, G., (2010) Surface Diffusion: Metals, Metal Atoms, and Clusters, , Cambridge Univesrity Press, New YorkKim, S.Y., Lee, I.-H., Jun, S., (2007) Phys. Rev. B: Condens. Matter Mater. Phys., 76, p. 245407Liu, Y.B., Sun, D.Y., Gong, X.G., (2002) Surf. Sci., 498, pp. 337-342Prévot, G., Barbier, L., Steadman, P., (2010) Surf. Sci., 604, pp. 1265-1272Pedersen M.Ø, Helveg, S., Ruban, A., Stensgaard, I., Lægsgaard, E., Nørskov, J.K., Besenbacher, F., (1999) Surf. Sci., 426, pp. 395-409Gohda, Y., Groß, A., (2007) Surf. Sci., 601, pp. 3702-3706Pastor, E., Rodriguez, J.L., Iwasita, T., (2002) Electrochem. Commun., 4, pp. 959-962Keister, J.K., Rowe, J.E., Kolodziej, J.J., Madey, T.E., (2000) J. Vac. Sci. Tech. B, 18, pp. 2174-2178. , 10.1116/1.1305872Martin, R., Gardner, P., Bradshaw, A.M., (1995) Surf. Sci., 342, pp. 69-84Bare, S.R., Hofmann, P., King, D.A., (1984) Surf. Sci., 144, pp. 347-369Yamagishi, S., Fujimoto, T., Inada, Y., Orita, H., (2005) J. Phys. Chem. B, 109, pp. 8899-8908Watanabe, S., Inukai, J., Ito, M., (1993) Surf. Sci., 293, pp. 1-9Sarkar, A., Kerr, J.B., Cairns, E.J., (2013) ChemPhysChem, 14, pp. 2132-2142Du, B., Zaluzhna, O., Tong, Y.J., (2011) Phys. Chem. Chem. Phys., 13, pp. 11568-11574Auten, B.J., Lang, H., Chandler, B.D., (2008) Appl. Catal., B, 81, pp. 225-235Gohda, Y., Groß, A., (2007) J. Electroanal. Chem., 607, pp. 47-53Kobiela, T., Moors, M., Linhart, W., Cebula, I., Krupski, A., Becker, C., Wandelt, K., (2010) Thin Solid Films, 518, pp. 3650-3657Petkov, V., Wanjala, B.N., Loukrakpam, R., Luo, J., Yang, L., Zhong, C.-J., Shastri, S., (2012) Nano Lett., 12, pp. 4289-4299Authors thank Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP-07/54829-5) and Conselho Nacional de Pesquisa (CNPq) for financial support. Specially thank to L. H. Lima for experimental assistance with STM measurements and Prof. G. Tremiliosi-Filho for lending the Au(332) crystal. MJP, SF and EAC thank FAPESP and CNPq for the fellowships granted (Procs. FAPESP 2011/12.566-3 and 2012/16860-6; Proc. CNPq 160172/2011-0)

Intramolecular coupling of terminal alkynes by atom manipulation

Glaser-like coupling of terminal alkynes by thermal activation is extensively used in on-surface chemistry. Here we demonstrate an intramolecular version of this reaction performed by atom manipulation. We used voltage pulses from the tip to trigger a Glaser-like coupling between terminal alkyne carbons within a custom synthesized precursor molecule adsorbed on bilayer NaCl on Cu(111). Different conformations of the precursor molecule and the product were characterized by molecular structure elucidation with atomic force microscopy and orbital density mapping with scanning tunneling microscopy, accompanied by density functional theory calculations. We revealed partially dehydrogenated intermediates providing insight into the reaction pathway

Self-assembly Of Nitpp On Cu(111): A Transition From Disordered 1d Wires To 2d Chiral Domains.

The growth and self-assembling properties of nickel-tetraphenyl porphyrins (NiTPP) on the Cu(111) surface are analysed via scanning tunnelling microscopy (STM), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT). For low coverage, STM results show that NiTPP molecules diffuse on the terrace until they reach the step edge of the copper surface forming a 1D system with disordered orientation along the step edges. The nucleation process into a 2D superstructure was observed to occur via the interaction of molecules attached to the already nucleated 1D structure, reorienting molecules. For monolayer range coverage a 2D nearly squared self-assembled array with the emergence of chiral domains was observed. The XPS results of the Ni 2p(3/2) core levels exhibit a 2.6 eV chemical shift between the mono- and multilayer configuration of NiTPP. DFT calculations show that the observed chemical shifts of Ni 2p(3/2) occur due to the interaction of 3d orbitals of Ni with the Cu(111) substrate.1718344-1835

Bistability between π -diradical open-shell and closed-shell states in indeno[1,2- a ]fluorene

Indenofluorenes are non-benzenoid conjugated hydrocarbons that have received great interest owing to their unusual electronic structure and potential applications in nonlinear optics and photovoltaics. Here we report the generation of unsubstituted indeno[1,2-a]fluorene on various surfaces by the cleavage of two C–H bonds in 7,12-dihydroindeno[1,2-a]fluorene through voltage pulses applied by the tip of a combined scanning tunnelling microscope and atomic force microscope. On bilayer NaCl on Au(111), indeno[1,2-a]fluorene is in the neutral charge state, but it exhibits charge bistability between neutral and anionic states on the lower-workfunction surfaces of bilayer NaCl on Ag(111) and Cu(111). In the neutral state, indeno[1,2-a]fluorene exhibits one of two ground states: an open-shell π-diradical state, predicted to be a triplet by density functional and multireference many-body perturbation theory calculations, or a closed-shell state with a para-quinodimethane moiety in the as-indacene core. We observe switching between open- and closed-shell states of a single molecule by changing its adsorption site on NaCl

Direct visualization of individual aromatic compound structures in low molecular weight marine dissolved organic carbon

Dissolved organic carbon (DOC) is the largest pool of exchangeable organic carbon in the ocean. However, less than 10% of DOC has been molecularly characterized in the deep ocean to understand DOC’s recalcitrance. Here we analyze the radiocarbon (14C) depleted, and presumably refractory, low molecular weight (LMW) DOC from the North Central Pacific using atomic force microscopy to produce the first atomic-resolution images of individual LMW DOC molecules. We evaluate surface and deep LMW DOC chemical structures in the context of their relative persistence and recalcitrance. Atomic force microscopy resolved planar structures with features similar to polycyclic aromatic compounds and carboxylic-rich alicyclic structures with less than five aromatic carbon rings. These compounds comprise 8% and 20% of the measurable molecules investigated in the surface and deep, respectively. Resolving the structures of individual DOC molecules represents a step forward in molecular characterization of DOC and in understanding its long-term stability

Construção de nanoestruturas de tetrafenil porfirinas e ftalocianinas em superfícies metálicas

Orientador: Abner de SiervoDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb WataghinResumo: O estudo de sistemas moleculares em cima de substratos metálicos tem atraído uma crescente atenção da comunidade científica. O melhor entendimento sobre as características de auto-organização e a habilidade de controlá-las em moléculas tem gerado formas mais baratas e rápidas de usar a abordagem bottom-up em nanociência. Dentre os diversos estudos feitos, podemos citar o desenvolvimento de sensores de gás que utilizam do sinal magnético de uma camada auto-organizada de moléculas e da ligação de pequenas moléculas como CO ou NO que promovem a emergência de magnetismo na amostra. Outro aspecto interessante do estudo de sistemas moleculares se encontra na similariedade das moléculas que podem ser utilizadas com moléculas encontradas nos processos recorrentes na natureza, por exemplo, as clorofilas e hemoglobinas. Isto significa que ao estudar moléculas simples é possível mimetizar um comportamento parecido com o das moléculas citadas. Neste sentido, em nosso trabalho estudamos dois tipos de moléculas ¿ Porfirinas e Ftalocianinas ¿ e as propriedades estruturais quando depositadas em diferentes substratos metálicos. As porfirinas foram analisadas em uma superfície de baixo índice de Miller, Cu(111), e tiveram seu comportamento comparado com o análogo em superfícies vicinais, Au(332) e Au(788). As porfirinas formam estruturas em 1D quando depositadas em pequenas quantidades, dependendo da natureza do substrato e a largura de seu terraço. Em maiores coberturas, as porfirinas formam diferentes estruturas de empacotamento fechado em 2D, de simetrias quadrada e paralelogrâmica. Eletronicamente observou-se a modificação do entorno químico do níquel quando a molécula de NiTPP é adsorvida no Cu(111). As ftalocianinas foram depositadas em diferentes substratos visando a produção de co-organização de dois tipos de moléculas num padrão tabuleiro de xadrez. Após a obtenção do padrão de tabuleiro de xadrez, nós realizamos experimentos para elucidar os mecanismos que possibilitam formar tais estruturas. Com o intuito de estudar auto-organização molecular, nós empregamos técnicas sensíveis a superfícies como a Microscopia de Tunelamento, Espectroscopia de Tunelamento e Espectroscopia de Fotoemissão por Raios-X. Tais técnicas possibilitam a obtenção das propriedades estruturais e eletrônicas das nanoestruturas formadasAbstract: The study of molecular systems on top of metal substrates has gathered increased atten-tion of the scientific community. Better understanding over different self-assembly haracteristics and the ability to control them in molecules has led to the development of quicker and cheaper routes of the use of the bottom-up approach in nanoscience. Among the diverse studies, we can cite the development of gas sensors that use the mag-netic signal of a self-assembled layer of molecules and the eventual binding of small molecules such as CO or NO leading to the emergence of magnetism on the sample. Another interesting aspect of the study of molecular systems is the similarity of molecules commonly used with molecules found in nature processes, e.g. chlorophylls and hemeglobins. This means that by studying simple molecules one can try to mimic the natural processes of those natural molecules. In this sense, in our work we have studied two classes of molecules ¿ Porphyrins and Phthalocyanines ¿ and their structural properties when deposited on different metal substrates. The porphyrins were analyzed on a low-index miller surface, Cu(111) and compared to their be-havior when deposited on vicinal substrates, Au(332) and Au(788). The porphyrins were ob-served to form 1D structures when deposited in small quantities depending on the nature of the substrate and its terrace width. At higher coverages, porphyrins formed different close-packed 2D structures, with square and parallelogram symmetry. Electronically was observed the modifica-tion of the chemical environment of nickel when NiTPP is adsorbed on Cu(111). The phthalo-cyanines were deposited on different substrates as well, towards the goal of producing co-assembling of two types of molecules as chessboard arrays. After the chessboard array was obtained, we gathered knowledge about the mechanisms that formed such structures. Towards the goal of studying molecular self-assembly, we have employed proper surface sensitive techniques such as Scanning Tunneling Microscopy, Scanning Tunneling Spectroscopy and X-Ray Photoelectron Spectroscopy. Such techniques allowed us to obtain the structural and electronic properties of the nanostructures formedMestradoFísicaMestre em Físic

Probing Molecular Excited States by Atomic Force Microscopy

By employing single charge injections with an atomic force microscope, we investigated redox reactions of a molecule on a multilayer insulating film. First, we charged the molecule positively by attaching a single hole. Then we neutralized it by attaching an electron and observed three channels for the neutralization. We rationalize that the three channels correspond to transitions to the neutral ground state, to the lowest energy triplet excited states and to the lowest energy singlet excited states. By single-electron tunneling spectroscopy we measured the energy differences between the transitions obtaining triplet and singlet excited state energies. The experimental values are compared with density functional theory calculations of the excited state energies. Our results show that molecules in excited states can be prepared and that energies of optical gaps can be quantified by controlled single-charge injections. Our work demonstrates the access to, and provides insight into, ubiquitous electron-attachment processes related to excited-state transitions important in electron transfer and molecular optoelectronics phenomena on surfaces

Intramolecular Coupling of Terminal Alkynes by Atom Manipulation

Glaser‐like coupling of terminal alkynes by thermal activation is extensively used in on‐surface chemistry. Here we demonstrate an intramolecular version of this reaction performed by atom manipulation. We used voltage pulses from the tip to trigger a Glaser‐like coupling between terminal alkyne carbons within a custom‐synthesized precursor molecule adsorbed on bilayer NaCl on Cu(111). Different conformations of the precursor molecule and the product were characterized by molecular structure elucidation with atomic force microscopy and orbital density mapping with scanning tunneling microscopy, accompanied by density functional theory calculations. We revealed partially dehydrogenated intermediates, providing insight into the reaction pathwayWe thank the European Union (Project SPRING, contract no. 863098), the ERC grant AMSEL (682144), the Spanish Agencia Estatal de Investigación (MAT2016-78293-C6-3-R and CTQ2016-78157-R), Xunta de Galicia (Centro de Investigación de Galicia accreditation 2019–2022, ED431G 2019/03) and the EuropeanRegional Development Fund-ERDF for financial supportS