Growth and Structure of Crystalline Silica Sheet on Ru(0001)

Abstract

Thin SiO 2 films were grown on a Ru(0001) single crystal and studied by photoelectron spectroscopy, infrared spectroscopy and scanning probe microscopy. The experimental results in combination with density functional theory calculations provide compelling evidence for the formation of crystalline, double-layer sheet silica weakly bound to a metal substrate. DOI: 10.1103/PhysRevLett.105.146104 PACS numbers: 68.35.Àp, 68.47.Gh, 68.55.Àa Silicon dioxide (SiO 2 ) plays a key role in many modern technologies and applications that range from insulating layers in integrated circuits to supports for metal and oxide clusters in catalysts. For better understanding of structureproperty relationships on silica-based materials, particularly of reduced dimensions, thin silica films grown on metal single crystal substrates are suggested as suitable model systems that allow the facile application of many ''surface science'' techniques. It has recently been shown that crystalline silica films and nanowires can be grown on Mo(112) [1][2][3][4][5]. The ultrathin film consists of a monolayer honeycomblike network of corner-sharing [SiO 4 ] tetrahedra, thus resulting in a SiO 2:5 stoichiometry of the film. The Si atoms in these films can be partly substituted by Al in the course of preparing metal supported aluminosilicate films [6], which is the first step towards experimental modeling of catalytic centers in zeolitelike materials. However, attempts to grow thicker silica films on the Mo substrates resulted in amorphous structures [7][8][9], most likely due to the formation of strong Si-O-Mo bonds at the interface that govern the growth mode [9]. Recently, the preparation of crystalline silica films on other supports such as Pd(100) [10] and Ni(111) [11] has been reported. However, the atomic structure of the films, film surface termination, and the nature of the silica-metal interface were not determined.In this Letter, we report on the preparation and the atomic structure of well-defined silica films on Ru(0001). The experimental results, obtained by photoelectron and vibrational spectroscopies and high-resolution scanning probe microscopy, are complemented by density functional theory calculations which together provide compelling evidence for the formation of a double-layer sheet silicate, with a SiO 2 stoichiometric composition, weakly bound to a metal support. The results open new perspectives for employing a ''surface science'' approach to understand the reactivity of silicate surfaces consisting of hydrophobic Si-O-Si bonds, such as those of microporous all-silica zeolites [12]. Also, these films can be used as model supports for catalytically active metal and oxide clusters [4,13].The experiments were performed in an ultrahigh vacuum chamber equipped with low energy electron diffraction (LEED) and Auger electron spectroscopy, x-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy (IRAS), and scanning tunneling microscopy (STM). Atomically resolved atomic force microscopy (AFM) and STM image...

Oxidation of the Ru(0001) surface covered by weakly bound, ultrathin silicate films

“…In addition, this film was prepared using isotopically labelled molecular oxygen, 18 O 2 . As expected, a new broad band centered at 1190 cm -1 is observed in IRA-spectrum which is characteristic for three-dimensional, bulk-like ( 18 O-labeled) silica [1,7,9] (see Fig. S2), suggesting that this sample contains also some silica nanoparticles.…”

“…It is well established that the thinnest silica film forms a hexagonal layer of corner-sharing [SiO 4 ] tetrahedra (referred to as "silicatene" in analogy to graphene [5]) which is strongly bound to a metal support through Si-O-Metal linkages [6]. On noble metals such as Ru(0001), Pd(100) and Pt(111), double-layer (or bilayer) silicate films may be grown, which are weakly bound to the support via dispersive forces [7][8][9][10]. In this case, a relatively large space between the silicate sheet and the metal support allows, in principle, small molecules to intercalate the interface, diffuse and ultimately react on the metal surface.…”

Exploring Zeolite Chemistry with the Tools of Surface Science: Challenges, Opportunities, and Limitations

“…17 This film was synthesized based on a preparation of silica (SiO 2 ) bilayer structure first reported by Löffler et al 18 . Using Si and Al co-deposition, some of the Si atoms in the silica film can be replaced by Al, thus resulting in aluminosilicate films.…”

Models for heterogeneous catalysts: studies at the atomic level

“…The stoichiometry of this film is SiO 2.5 . However, on the latter metal surface, a bi-layer film may also be formed, as demonstrated in 2010 by D. Löffler et al (2010), which has SiO 2 stoichiometry, and is only bound to the metal substrate by dispersive forces. The network formed, as viewed from above (e.g., by STM) is identical to the monolayer, but the vibrational spectrum, as also shown in Fig.…”