Zinc oxide in the form of nanoscale materials can be regarded as one of the most important semiconductor oxides at present. However, the question of how chemical defects influence the properties of nanoscale zinc oxide materials has seldom been addressed. In this paper, we report on the introduction of defects into nanoscale ZnO, their comprehensive analysis using a combination of techniques (powder X‐ray diffraction (PXRD), X‐ray absorption spectroscopy/extended X‐ray absorption fine structure (XAS/EXAFS), electron paramagnetic resonance (EPR), magic‐angle spinning nuclear magnetic resonance (MAS‐NMR), Fourier‐transform infrared (FTIR), UV‐vis, and photoluminescence (PL) spectroscopies coupled with ab‐initio calculations), and the investigation of correlations between the different types of defects. It is seen that defect‐rich zinc oxide can be obtained under kinetically controlled conditions of ZnO formation. This is realized by the thermolysis of molecular, organometallic precursors in which ZnO is pre‐organized on a molecular scale. It is seen that these precursors form ZnO at low temperatures far from thermodynamic equilibrium. The resulting nanocrystalline ZnO is rich in defects. Depending on conditions, ZnO of high microstructural strain, high content of oxygen vacancies, and particular content of heteroatom impurities can be obtained. It is shown how the mentioned defects influence the electronic properties of the semiconductor nanoparticles.

Is this place taken? A mechanism has been proposed for the formation of methanol from CO and H2 on ZnO surfaces in which CO is adsorbed at oxygen vacancies on the heterogeneous catalyst (see picture: C red, H white, O gray, Zn black). The active sites are blocked when CO2 is added to the gas mixture.

The determination of the structure of inhomogeneous metal-oxide surfaces represents a formidable task. With the present study, we demonstrate that using the binding energy of a probe molecule, CO, is a reliable tool to validate structural models for such complex surfaces. Combining several types of first-principles calculations with advanced molecular beam methods, we are able to provide conclusive evidence that the polar O-terminated surface of ZnO is either reconstructed or hydrogen covered. This finding has important consequences for the ongoing discussion regarding the stabilization mechanism of the electrostatically unstable ("Tasker type 3") polar ZnO surfaces.

We report on theoretical and experimental work involving a particular molecular switch, an [Fecomplex, that utilizes a spin transition ("crossover"). The hallmark of this transition is a change of the spin of the metal ion, S Fe = 0 to S Fe = 2, at fixed oxidation state of the Fe ion. Combining density functional theory and first principles calculations, we demonstrate that within a single molecule this transition can be triggered by charging the ligands. In this process the total spin of the molecule, combining metal ion and ligands, crosses over from S = 0 to S = 1. Three-terminal transport through a single molecule shows indications of this transition induced by electric gating. Such an electric field control of the spin transition allows for a local, fast, and direct manipulation of molecular spins, an important prerequisite for molecular spintronics.

The role of defects on oxide surfaces, especially that of oxygen defects, has been always considered crucial for the interfacial chemistry of such substrates . Recently, considerable progress has been achieved in this field in particular for the case of titanium dioxide (TiO 2 ) by the combination of scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. In fact it was possible to study a number of different reactions in considerable detail, including H 2 O dissociation, [1,2] O 2 dissociation, [2][3][4] and (de-)hydrogenation reactions of aromatic compounds. [5] Unfortunately, the experimental technique upon which this progress is largely based, STM, cannot be applied to powders, the technologically most important form of oxide materials. Although STM investigations of nanometer-sized powder particles have been reported in a (fairly small) number of cases, [6] the investigation of chemical reactions on oxide surfaces and the role of oxygen vacancies cannot be studied for nanoparticles in a straightforward fashion. On the other hand, infrared (IR) spectroscopy has been extensively applied to metal oxide powder samples, [7] but IR results on single-crystal oxides are rather scarce. As a result, the socalled surface science approach, which has been extremely successful for unraveling the mechanism of reactions on metal particles by comparison to results for well-understood singlecrystal reference systems, [8] has been severely hampered with regard to understanding reactions on oxide surfaces. Here, we present a novel method capable of investigating oxygen vacancies on surfaces of oxide single crystals as well as on powder particles. We apply this method to demonstrate that the surface chemistry of formaldehyde on TiO 2 nanoparticles is indeed determined by the density of O vacancies. We will first demonstrate that the presence of defect sites on surfaces of rutile TiO 2 (r-TiO 2 ) can be directly identified by ultrahighvacuum IR spectroscopy (UHV-FTIRS) using CO as a probe molecule. After calibrating this method using a well-defined single-crystal r-TiO 2 (110) substrate we will apply it to the corresponding powder samples.The reflection-absorption IR spectroscopy (RAIRS) data shown in Figure 1 demonstrate that on a fully oxidized r-TiO 2 (110) surface with a low density of defects only a single band at 2188 cm À1 is visible in the CO-stretching regime. This frequency is 45 cm À1 higher than that observed for the gas phase (2143 cm À1 ). Such a blue shift is typical for CO adsorbed on oxide surfaces and is in full accord with previous data from electron energy loss spectroscopy (EELS) and theoretical studies for CO adsorbed on the same substrate. [9] When we reduced the TiO 2 surface, either by controlled slightly sputtering or over-annealing at elevated temperatures, a second CO band was observed at 2178 cm À1 . In line with a recent STM study on r-TiO 2 (110) by Zhao et al. [10] the reduction-induced band at 2178 cm À1 is assigned to CO bound to Ti cations located in the vicinity of...

Single-molecule spintronics investigates electron transport through magnetic molecules that have an internal spin degree of freedom. To understand and control these individual molecules it is important to read their spin state. For unpaired spins, the Kondo effect has been observed as a low-temperature anomaly at small voltages. Here, we show that a coupled spin pair in a single magnetic molecule can be detected and that a bias voltage can be used to switch between two states of the molecule. In particular, we use the mechanically controlled break-junction technique to measure electronic transport through a single-molecule junction containing two coupled spin centres that are confined on two Co(2+) ions. Spin-orbit configuration interaction methods are used to calculate the combined spin system, where the ground state is found to be a pseudo-singlet and the first excitations behave as a pseudo-triplet. Experimentally, these states can be assigned to the absence and occurrence of a Kondo-like zero-bias anomaly in the low-temperature conductance data, respectively. By applying finite bias, we can repeatedly switch between the pseudo-singlet state and the pseudo-triplet state.

A mononuclear ruthenium(II) polypyridyl complex with an enlarged terpyridyl coordination cage was synthesized by the formal introduction of a carbon bridge between the coordinating pyridine rings. Structurally, the ruthenium(II) complex shows an almost perfect octahedral N6 coordination around the central Ru(II) metal ion. The investigation of the photophysical properties reveals a triplet metal-to-ligand charge transfer emission with an unprecedented quantum yield of 13% and a lifetime of 1.36 mus at room temperature and in the presence of air oxygen. An exceptional small energy gap between light absorption and light emission, or Stokes shift, was detected. Additionally, time-dependent density functional theory calculations were carried out in order to characterize the ground state and both the singlet and triplet excited states. The exceptional properties of the new compound open the perspective of exploiting terpyridyl-like ruthenium complexes in photochemical devices under ambient conditions.

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