18776 DOI: 10.1021/la102810m Langmuir 2010, 26(24), 18776–18787 Published on Web 11/15/2010 pubs.acs.org/Langmuir © 2010 American Chemical Society Growth Pattern of Ag n (n =1-8) Clusters on the r-Al 2 O 3 (0001) Surface: A First Principles Study Sandeep Nigam and Chiranjib Majumder* Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085, India Received July 15, 2010. Revised Manuscript Received October 1, 2010 We report an extensive first-principles study of the structure and electronic properties of Ag n (n =1-8) clusters isolated in gas phase and deposited on the R-Al 2 O 3 surface. We have used the plane wave based pseudopotential method within the framework of density functional theory. The electron ion interaction has been described using projector augmented wave (PAW), and the spin-polarized GGA scheme was used for the exchange correlation energy. The results reveal that, albeit interacting with support alumina, the Ag atoms prefers to remain bonded together suggesting an island growth motif is preferred over wetting the surface. When compared the equilibrium structures of Ag clusters between free and on alumina substrate, a significant difference was observed starting from n = 7 onward. While Ag 7 forms a three-dimensional (3D) pentagonal bipyramid in the isolated gas phase, on alumina support it forms a planar hexagonal structure parallel to the surface plane. Moreover, the spin moment of the Ag 7 cluster was found to be fully quenched. This has been attributed to higher delocalization of electron density as the size of the cluster increases. Furthermore, a comparison of chemical bonding analysis through electronic density of state (EDOS) shows that the EDOS of the deposited Ag n cluster is significantly broader, which has been ascribed to the enhanced spd hybridization. On the basis of the energetics, it is found that the adsorption energy of Ag clusters on the R-Al 2 O 3 surface decreases with cluster size. 1. Introduction Understanding the nature of cluster/metal-oxide interfaces constitutes one of the most appealing challenges nowadays for material scientists because of their important role in various technological applications such as metal-ceramic-based gas sen- sors, microelectronic devices and oxide-supported transition metal catalysts. 1-7 Oxide supports can significantly affect both structural and electronic characteristics of the cluster deposited on them. 2 In the past few years, diverse experimental 8-24 and theoretical studies 25-51 concerning deposition of metals on oxide surfaces have been reported. Reflection electron microscopy (REM) 10 and *E-mail: chimaju@barc.gov.in. (1) Goodman, D. W. Chem. Rev. 1995, 95, 523. (2) Gates, B. C. Chem. Rev. 1995, 95, 511. (3) Lambert, R. M.; Pacchioni, G., Eds. Chemisorptions and Reactivity on Supported Clusters and Thin Films: Towards an Understanding of Microscopic Processes in Catalysis; Kluwer: Dordrecht, 1997. (4) Lad, R. J. Surf. Rev. Lett. 1995, 12, 109. (5) Azad, A. M.; Akbar, S. A.; Mhaisalkar, S. G.; Birkefeld, L. D.; Goto, K. S. J. Electrochem. Soc. 1992, 139, 3690. (6) Kirner, U.; Schierbaum, K. D.; G€ opel, W.; Leibold, B.; Nicoloso, N.; Weppner, W.; Fischer, D.; Chu, W. F. Sens. Actuators, B 1990, 1, 103. (7) Gates, B. C.; Guczi, L.; Knozinger, H., Eds. Metal Clusters in Catalysis; Elsevier: Amsterdam, 1986. (8) Campbell, C. T.; Starr, D. E. J. Am. Chem. Soc. 2002, 124, 9212. Larsen, J. H.; Ranney, J. T.; Starr, D. E.; Musgrove, J. E.; Campbell, C. T. Phys. Rev. B 2001, 63, 195410. (9) Revenant, C.; Renaud, G.; Lazzari, R.; Jupille, J. Nucl. Instrum. Methods Phys. Res., Sect. B 2002, 246, 112. Suzuki, T.; Hishita, S.; Oyoshi, K.; Souda, R. Surf. Sci. 1999, 442, 291. (10) Ndubuisi, G. C.; Liu, J.; Cowley, J. M. Microsc. Res. Techniq. 1992, 20, 439. (11) Beitel, G.; Markert, K.; Wiechers, J.; Hrbek, J.; Behm, R. J. Adsorption on Ordered Surfaces of Ionic Solids and Thin Films; Springer- Verlag: Berlin, 1993; Vol 33, p 71.Bird, D. P. C.; de Castilho, C. M. C.; Lambert, R. M. Surf. Sci. 2000, 449, L221. (12) Canario, A. R.; Sanchez, E. A.; Bandurin, Y.; Esaulov, V. A. Surf. Sci. 2003, 547, L887. (13) Xu, C.; Lai, X.; Zajac, G. W.; Goodman, D. W. Phys. Rev. B 1997, 56, 13464. Negra, M.; Nicolaisena, N. M.; Lib, Z.; Møller, P. J. Surf. Sci. 2003, 540, 117. (14) Becker, C.; Von Bergmann, K.; Rosenhahn, A.; Schneider, J.; Wandelt, K. Surf. Sci. 2001, 486, L443. Nilius, N.; Corper, A.; Bozdech, G.; Ernst, N.; Freund, H. J. Prog. Surf. Sci. 2001, 67, 99. (15) Cai, Y. Q.; Bradshaw, A. M.; Guo, Q.; Goodman, D. W. Surf. Sci. 1998, 399, L357. (16) Luo, K.; Lai, X.; Yi, C. W.; Davis, K. A.; Gath, K. K.; Goodman, D. W. J. Phys. Chem. B 2005, 109, 4064. (17) Siani, A.; Wigal, K. R.; Alexeev, O. S.; Amiridis, M. D. J. Catal. 2008, 257, 16. (18) Gates, B. C. J. Mol. Catal., A: Chem. 2000, 163, 55. (19) Carrey, J.; Maurice, J. L.; Petroff, F.; Vaures, A. Surf. Sci. 2002, 504, 75. (20) Rossignol, C.; Arrii, S.; Morfin, F.; Piccolo, L.; Caps, V.; Rousset, J. L. J. Catal. 2005, 230, 476. (21) Biener, J.; Baumer, M.; Madix, R. J.; Liu, P.; Nelson, E.; Kendelewisz, T. Surf. Sci. 2000, 449, 50. (22) Gillet, E.; Yakhloufi, M. H. E.; Disalvo, J. P.; Abdelouahab, F. B. Surf. Sci. 1999, 419, 216. (23) Søndergarda, E.; Kerjan, O.; Abriou, D.; Jupille, J. Eur. Phys. J. D 2003, 24, 343. (24) Lazzari, R.; Jupille., J. Surf. Sci. 2001, 482-485, 823. (25) Sanz, J. F.; Marquez, A. J. Phys. Chem. C 2007, 111, 3949. (26) Bredow, T.; Pacchioni, G. Surf. Sci. 1999, 426, 106. (27) Sanz, J. F.; Hernandez, N. C.; Marquez, A. Theor. Chem. Acc. 2000, 104, 317. (28) Pillay, D.; Hwang, G. S. J. Mol. Struct. (THEOCHEM) 2006, 771, 129. (29) Barcaro, G.; Fortunelli, A. J. Phys. Chem. C 2007, 111, 11384. (30) Hu, Y. L.; Zhang, W. B.; Deng, Y. H.; Tang, B. Y. Comput. Mater. Sci. 2008, 42, 43. (31) Zhukovskii, Y. F.; Kotomin, E. A.; Borstel, G. Vacuum 2004, 74, 235. (32) Zhukovskii, Y. F.; Kotomin, E. A.; Fuks, D.; Dorfman, S. Superlattices Microstruct. 2004, 36, 63. (33) Barcaro, G.; Fortunelli, A. Phys. Rev. B 2007, 76, 165412. (34) Hernandez, N. C.; Sanz, J. F. J. Phys. Chem. B 2002, 106, 11495. (35) Hernandez, N. C.; Sanz, J. F. Appl. Surf. Sci. 2004, 238, 228. (36) Sanz, J. F.; Hernandez, N. C. Phys. Rev. Lett. 2005, 94, 016104. (37) Hernandez, N. C.; Graciani, J.; Marquez, A.; Sanz, J. F. Surf. Sci. 2005, 575, 189. (38) Hernandez, N. C.; Marquez, A.; Sanz, J. F.; Gomes, J. R. B.; Illas, F. J. Phys. Chem. B 2004, 108, 15671. (39) Rivanenkov, V. V.; Nasluzov, V. A.; Shor, A. M.; Neyman, K. M.; Reosch, N. Surf. Sci. 2003, 525, 173. (40) Gomes, J. R. B.; Illas, F.; Hernandez, N. C.; Sanz, J. F.; Wander, A.; Harrison, N. M. J. Chem. Phys. 2002, 116, 1688. (41) Lodziana, Z.; Nørskov, J. K. J. Chem. Phys. 2001, 115, 11261. (42) Yang, R.; Rendell, A. P. J. Phys. Chem. B 2006, 110, 9608. (43) Hinnemann, B.; Carter, E. A. J. Phys. Chem. C 2007, 111, 7105. (44) Meyer, R.; Lockemeyer, J.; Yeates, R.; Lemanski, M.; Reinalda, D.; Neurock, M. Chem. Phys. Lett. 2007, 449, 155. Meyer, R.; Ge, Q.; Lockemeyer, J.; Yeates, R.; Lemanski, M.; Reinalda, D.; Neurock, M. Surf. Sci. 2007, 601, 134. (45) Chatterjee, A.; Niwa, S.; Mizukami, F. J. Mol. Graph. Model. 2005, 23, 447. (46) Xiao, L.; Schneider, W. F. Surf. Sci. 2008, 602, 3445. (47) Gomes, J. R. B.; Lodziana, Z.; Illas, F. J. Phys. Chem. B 2003, 107, 6411. (48) Sanz, J. F.; Hernandez, N. C. Phys. Rev. Lett. 2005, 94, 016104. Hernandez, N. C.; Sanz, J. F. J. Phys. Chem. B 2001, 105, 12111. (49) Nasluzov, V. A.; Rivanenkov, V. V.; Shor, A. M.; Neyman, K. M.; Reosch, N. Chem. Phys. Lett. 2003, 374, 487. (50) Zhou, C.; Wu, J.; Kumar, T. J. D.; Balakrishnan, N.; Forrey, R. C.; Cheng, H. J. Phys. Chem. C 2007, 111, 13786.