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...

A combination of density functional theory calculations and photoelectron spectroscopy provides new insights into the atomistic picture of ultrathin silica films grown on Ru(0001). The silica film features a double-layer silicate sheet formed by corner-sharing [SiO 4 ] tetrahedra and is weakly bound to the Ru(0001) substrate. This allows oxygen atoms to reversibly adsorb directly on the metal surface underneath the silica film. We demonstrate that the amount of adsorbed oxygen can be reversibly varied by vacuum annealing and oxidation, which in turn result in gradual changes of the silica/Ru electronic states. This finding opens the possibility for tuning the electronic properties of oxide/metal systems without altering the thickness or the structure of an oxide overlayer.

The influence of the support material of vanadia catalysts on the reaction rate, activation energies, and defect formation enthalpies was investigated for the oxidative dehydrogenation of ethanol and propane. Characterization by infrared absorption–reflection spectroscopy (IRAS), Raman and UV–vis spectroscopy verifies a high dispersion of vanadia for powder and thin-film model catalysts. The support effect of ceria, alumina, titania, and zirconia is reflected in activation energy, oxidative dehydrogenation (ODH) rate, and temperature-programmed reductions (TPR) for both catalyst systems, ethanol and propane. Impendence spectroscopy and density functional theory (DFT) calculations were used to determine the defect formation enthalpy of the vanadyl oxygen double bond, providing the scaling parameter for a Bell–Evans–Polanyi relationship. On the basis of a Mars–van-Krevelen mechanism, an energy profile for the oxidative dehydrogenation is proposed

We demonstrate that photochemical functionalization can be used to functionalize and photopattern the surface of gallium nitride crystalline thin films with well-defined molecular and biomolecular layers. GaN(0001) surfaces exposed to a hydrogen plasma will react with organic molecules bearing an alkene (C=C) group when illuminated with 254 nm light. Using a bifunctional molecule with an alkene group at one end and a protected amine group at the other, this process can be used to link the alkene group to the surface, leaving the protected amine exposed. Using a simple contact mask, we demonstrate the ability to directly pattern the spatial distribution of these protected amine groups on the surface with a lateral resolution of <12 mum. After deprotection of the amines, single-stranded DNA oligonucleotides were linked to the surface using a bifunctional cross-linker. Measurements using fluorescently labeled complementary and noncomplementary sequences show that the DNA-modified GaN surfaces exhibit excellent selectivity, while repeated cycles of hybridization and denaturation in urea show good stability. These results demonstrate that photochemical functionalization can be used as an attractive starting point for interfacing molecular and biomolecular systems with GaN and other compound semiconductors.

Surface chemical changes or passivation can be used to enhance the electrical performance of device structures. The solution-based (NH4)2S x treatment of ZnO single crystals of (0001), (101̅0), and (0001̅) orientations as well as ZnO nanorods was studied by using X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS). The (101̅0) and (0001̅)-oriented single crystals and ZnO nanorods each showed evidence that the ZnO was consumed, forming a ZnS layer at the surface. In contrast, the ZnO (0001) crystal did not substantially react with the sulfide solution. However, the surface hydroxyl species were displaced by a sulfide passivation layer of 0.21 ML. This process resulted in an apparent increase in upward band bending by ∼0.1−0.3 eV. P3HT−ZnO photovoltaic devices fabricated on O-polar single crystals showed electrical properties which can be correlated with ZnS formation due to the sulfide treatment.