ISSN 1063-7834, Physics of the Solid State, 2010, Vol. 52, No. 3, pp. 641–648. © Pleiades Publishing, Ltd., 2010. Original Russian Text © K.M. Tsysar’, D.I. Bazhanov, A.M. Saletsky, V.S. Stepanyuk, W. Hergert, 2010, published in Fizika Tverdogo Tela, 2010, Vol. 52, No. 3, pp. 593–599. 641 1. INTRODUCTION Unique physical properties of nanostructures, such as the magnetism, quantum conductance, and high adsorption capacity, have attracted the particular attention of many scientific groups around the world. Investigations of properties of one-dimensional nano- structures, i.e., nanocontacts and nanowires, are of special interest. These structures are spontaneously formed during the operation of a scanning tunneling microscope between the microscope probe and the surface under investigation and also at points of frac- ture of solid crystals [1–3]. One of the unique proper- ties of one-dimensional nanostructures is the quan- tum electronic conductance that manifests itself already at room temperature. In these structures, the current can be carried by only one electron [4–8]. Investigations of the electronic properties of one- dimensional nanostructures occupy an important place in modern research [9–13]. The experimental data confirm the theoretically predicted quantum nature of conductance of nanocontacts [3]: the con- ductance takes on integer values multiple to the con- ductance quantum G 0 = 2e 2 /h, where e is the elemen- tary charge and h is the Planck constant. However, there are a number of works in which the authors observed that the conductance deviates from integer values [13, 14]. This phenomenon is explained by the possible interaction with impurity atoms and mole- cules, which in small numbers can always be present in experiments [15, 16]. In the interaction, these impuri- ties can strongly affect the nanostructures and change their atomic and, correspondingly, electronic struc- tures and, as a result, their physical properties [17– 20]. In this case, the presence of impurities can lead to the destruction or stabilization of the structure, i.e., to an increase in its strength [19]. Therefore, the investi- gation of the influence of impurity atoms and mole- cules on the properties of nanostructures is the most important problem of physics and chemistry of low- dimensional systems. In recent years, the attention of many scientific groups has been focused on theoretical and experimental investigations into the influence of impurities on palladium, gold, silver, and platinum nanocontacts and nanowires [3, 17–20]. The properties of the atomic and electronic struc- tures of palladium nanocontacts have been investi- gated beginning with the experimental work by Matsuda and Kizuka [3], who were the first to produce a stable palladium nanocontact at room temperature by using the scanning tunneling microscope. It was also found in [3] that the palladium contacts have a quantum tunneling conductance. Subsequently, in many theoretical works, the authors studied in detail the atomic structure and electronic properties of one- dimensional palladium systems, obtained results on the conductance of palladium nanocontacts [5, 6, 15], and examined their magnetic properties [12, 21–23]. However, in these works, the properties of one-dimen- sional palladium structures were studied in the absence of impurities. At the same time, it has been Effect of Hydrogen Impurity Atoms and Molecules on the Atomic Structure of Palladium Nanocontacts K. M. Tsysar’ a, *, D. I. Bazhanov a , A. M. Saletsky a , V. S. Stepanyuk b , and W. Hergert c a Lomonosov Moscow State University, Moscow, 119992 Russia * e-mail: smelova_k_m@mail.ru b Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, Halle, D-06120 Germany c Fachbereich Physik, Martin-Luther-Universität, Friedemann-Bach-Platz 6, Halle-Wittenberg, Halle, D-06108 Germany Received March 24, 2009; in final form July 17, 2009 Abstract—The interaction of hydrogen impurity atoms and molecules with palladium nanocontacts and its effect on the atomic structure and strength of the nanocontacts have been studied using the computer simu- lation. It has been revealed that the sorption of hydrogen atoms and molecules increases the specific cohesive energy between the palladium atoms nearest to the hydrogen atom in the chain of the nanocontact, which leads to an increase in the strength of the palladium nanocontact. An analysis of the electronic structure of the palladium nanocontact in the presence of the hydrogen molecule has demonstrated that the strong inter- action of the molecule with the contact can result in its disassociation due to the hybridization of the s and d orbitals of palladium and the s orbitals of hydrogen atoms upon sorption in the nanocontact chain. DOI: 10.1134/S1063783410030285 LOW-DIMENSIONAL SYSTEMS AND SURFACE PHYSICS