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Financial support from the Deutsche Forschungsgemeinschaft within SFB 569, the Belgium Odysseus and Interuniversity Attraction Pole programs, the Swiss National Science Foundation, and the NCCR "Nanoscale Science" is gratefully acknowledged. The authors also thank Dr. G. Kastle for fruitful discussions and J. Baccus for technical assistance.

Adv. Mater. 2008, 20, 1–5 2008 WILEY-VCH Verlag Gmb Small organic molecules as potential building-blocks for future nanoelectronic devices will require new types of sensors able to identify/quantify molecules in appropriate solutions on a single-molecule level. Recently, an elegant new method has been proposed that allows detection of small aromatic units like 4aminothiophenol (4-ATP) molecules by measuring the tunneling resistance between two metal electrodes separated by a short distance (a few nanometers). While, from a simple point of view, an increase in conductivity should be expected because of the bridging of the tunnelling gap by one or more molecules (thus offering molecular orbitals as additional transport channels), a decreased conductivity was observed experimentally with a reduction factor that depended on the type of molecule present in the solution. Here, we report on combined experimental and theoretical efforts aimed at unravelling this phenomenon by studying the electronic properties of one of themetal electrodes in such a molecular junction. For this purpose, a 4-ATP self-assembledmonolayer (SAM) has been prepared on top of a Au(111) crystal, which, in a second step, has been metallized by a nearly closed Pd overlayer of monoatomic height by means of a recently developed electrochemical approach. Photoelectron spectroscopy together with density functional theory (DFT) taking into account all contributing parts of the molecular junction finally allowed analysis of its structural setup and its electronic properties. Angle-resolved X-ray photoelectron spectroscopy (XPS) reveals that the 4-ATP SAM actually consists of a minimum of two molecular layers. Most importantly, using ultraviolet photoelectron spectroscopy (UPS) and DFT simulations, strong chemical interactions between the metal overlayer and the amino groups are found to play a decisive role in determining the overall electronic properties, and thus the transport properties of the SAM/metal contact, as will be demonstrated in the following. It is well-known that 4-ATP has a strong tendency to form multilayers on Au(111), which lead to scanning tunnelling microscopy (STM) images with considerable height variations and of blurred contrast when it comes to molecular-scale resolution. Even for highly diluted solutions (sub-millimolar concentrations of the 4-ATP), more than just one layer is generally formed. On the other hand, reductive desorption of thiols from gold surfaces is known to occur at electrode potentials negative of 0.1 V vs. standard calomel electrode (SCE), which may be considered an appropriate means for desolving any thiol in excess of the first layer. In Figure 1 cyclic voltammograms are shown for Au(111) in 0.1 M H2SO4, after the electrode had been immersed for 15min in a 0.1 10 3 M 4-ATP/0.1 M H2SO4 modification solution. While the first cycle (dash-dotted line, start at þ0.2 V vs. SCE in the negative direction) was restricted to the stability range of the 4-ATP adlayer, i.e., 0 and þ0.4 V, the second cycle (solid line) was extended to much more negative potentials to explore partial reductive desorption. The latter process is clearly reflected in a cathodic current that peaks at 0.18V. The third cycle (dotted line) now shows double-layer charging behaviour up

At the ultimate limit of magnetic recording, suitable storage media will consist of nanometer-sized entities, each of which will carry one bit of information. Materials with a high magnetocrystalline anisotropy energy are required to guarantee thermal stability of the ferromagnetic state at realistic operating temperatures. The face-centered tetragonal (fct) L10 FePt alloy belongs to the promising class of materials that offer the perspective of storing one magnetic bit per nanoparticle. Widespread activities have therefore arisen worldwide, targeting novel strategies for both the synthesis of suitable magnetic nanostructures and their organization into superlattices by means of parallel processes. Here, we present a new approach for the synthesis of size-selected L10 FePt nanoparticles based on the self-organization of spherical micelles formed by diblock copolymers, thereby significantly extending a previous technique to produce large-scale arrays of elemental nanoparticles. Our approach overcomes the typical drawbacks of the current colloidal routes towards densely packed arrays of ferromagnetic FePt nanoparticles while still guaranteeing areal densities exceeding 1 Tbits inch (1 inch≈ 2.54 cm). Since the first presentation of magnetic data-storage devices five decades ago, the areal density of digital information has increased by eight orders of magnitude to reach values of about 200 Gbits inch, as found in present hard disk drives. A few years ago, an efficient method was developed to synthesize FePt nanoparticles on the basis of wet-chemical synthesis (hereafter referred to “colloidal”), which involves particle stabilization by an organic-ligand shell. The significant advantage of this approach, allowing a simple preparation of densely packed 2D nanoparticle arrays from corresponding particle solutions, is, however, compensated by some serious drawbacks related to the thin ligand shell (1–3 nm) which serves as a spacer between the nanoparticles. As a consequence of the resulting small interparticle distance, the nanoparticles exhibit a strong tendency to aggregate during heat treatments. Thermal annealing at 500–600 °C is, however, generally required in order to transform the assynthesized, chemically disordered (Fe and Pt atoms randomly distributed over the lattice sites) face-centered cubic (fcc) structure, which results in superparamagnetic behavior, into the magnetically attractive L10 phase. Furthermore, undesirable collective magnetic dynamics arise at such small interparticle distances through dipolar coupling; collective modes, however, are clearly at odds with the idea of storing magnetic data in individual nanoparticles. Finally, the heat-treated colloidal FePt nanoparticles are found to be highly oxidized and contaminated by carbon because of the thermally induced decomposition of the organic shell. Recent alternative routes for the synthesis of L10 FePt nanoparticles include their formation in cluster beams and from wet-chemical procedures at elevated temperatures. However, even in these cases, the particles still need to be encapsulated with an organic-ligand shell, either after deposition from a cluster beam or during synthesis, to guarantee their ordered organization. Typical interparticle spacings are thus the same as described before, resulting in dipolar coupling and, additionally, the particle–ligand interactions can deteriorate the magnetic properties. Our new approach for generating ultrahigh-density arrays of L10 FePt nanoparticles overcomes all these drawbacks. It is based on the flexibility of macromolecular chemistry to design diblock copolymers with adjustable block lengths, which form reverse micelles when dissolved in an apolar solvent like toluene. After loading their cores with a suitable metal salt, such C O M M U N IC A TI O N

Ligand-free FePt nanoparticles are prepared in densely packed arrays (see Figure) under ultrahigh vacuum conditions, in which oxygen and hydrogen plasmas are used to remove the organic shells that are present after particle synthesis. The electronic structure and magnetic properties of the “bare”, face-centered-cubic FePt particles are presented. Applications in high-density magnetic data recording are foreseen.

The preparation of hexagonally ordered metallic nanodots was studied in detail with emphasis on the chemical state of the resulting particles. To obtain these dots, in a first step micellar structures were formed from diblock copolymers in solution. The reverse micelles themselves are capable of ligating defined amounts of a metal salt within their cores, acting as nanoreactors. After transfer of the metal-loaded reverse micelles onto a substrate, the polymer was removed by means of different plasmas (oxygen and/or hydrogen), which also allow the metal salt to be reduced to the metallic state. In this way, ordered arrays of metallic nanodots can be prepared on various substrates. By adjusting the appropriate parameters, the separation and the size of the dots can be varied and controlled. To determine their purity, chemical state, and surface cleanliness—all of which are crucial for subsequent experiments since nanoscale structures are intrinsically surface dominated—in-situ X-ray photoelectron spectroscopy (XPS) and ex-situ transmission electron microscopy (TEM) were applied, also giving information on the formation of the nanodots.

Natural type IIb diamond surfaces of (100), (110), and (111) orientation, as well as chemical vapor deposited (CVD) diamond thin films with (100), (110), or mixed orientation are probed by photoelectron spectroscopy in the ultraviolet (UPS) and X-ray (XPS) energy regimes. Dramatic changes can be observed in the valence band and core level spectra of these surfaces upon annealing, hydrogen-plasma exposure, or pulsed dye laser irradiation. The observed changes can be reversed by the exposure of the surfaces to atomic hydrogen (deuterium). The valence band spectra reveal specific surface reconstructions for all three surface preparation methods and moreover a cleaning effect is observed following laser irradiation of CVD diamond surfaces. A comparison to a multitude of theoretical and experimental studies on diamond surface reconstruction is made to elucidate the connection between electronic properties and atomic surface structures.

In the last fifteen years the necessity for efficient environmental protection has become generally accepted. However, before practical measures can be taken, a comprehensive assessment of the present environmental situation should be made, taking into consideration the risks involved in as well as the positive effects of any planned environmental changes—whether natural or man made. This clearly calls for close cooperation between the various scientific disciplines. For example, the treatment of exhaust fumes from motor vehicles has been of primary importance in measures taken to restrict the recent damage caused to woodland areas. The introduction of 3-Way-Catalyst technology has been regarded as a viable countermeasure. The following report is intended to describe a method for examining some side effects of catalyst usage. Accordingly, the chemical composition of microparticles emitted from combustion motors through the use of catalysts will be examined and some possible changes in the environment caused by such particles will be briefly considered. As in the area of research into catalysts for industrial synthesis a knowledge of the surface structure of such particles, i.e. the boundary layer between emission product and environment, is necessary in the investigation into their effects. Consequently, a surface sensitive technique from solid state physics, X-ray photoelectron spectroscopy (XPS or ESCA) has found novel use in the area of environmental analysis. In the following report emphasis will be placed on the description of measurement techniques and the interpretation of the results obtained. After a critical consideration of the experimental methods, examples from two different series of measurements on diesel and Otto motors equipped with soot filters or 3-way-catalysts respectively, will be given. Hopefully, this report will also stimulate establishment of the use of EPS in environmental research techniques.

In den letzten funfzehn Jahren wuchs die Einsicht in die Notwendigkeit eines effizienten Umweltschutzes. Konkrete Masnahmen setzen allerdings eine umfassende Analyse der gegebenen Umweltsituation und die Abschatzung sowohl der positiven Auswirkungen als auch der Risiken einer geplanten Veranderung voraus. Dies ist nur in einer fachubergreifenden Zusammenarbeit naturwissenschaftlicher Disziplinen moglich. Beispielsweise wird zur Eindammung der neuartigen Waldschaden die Entgiftung der Abgase von Kraftfahrzeugen als vorrangig erachtet, und die Dreiwegekatalysatortechnik wird dabei gegenwartig als ein geeignetes Mittel angesehen. In diesem Beitrag wird uber Versuche berichtet, die chemische Konstitution von Mikropartikeln, die aus Verbrennungsmotoren emittiert werden, aufzuklaren und eventuelle Veranderungen dieser Emission durch den Katalysator festzustellen. Da vor allem die Oberflache dieser Partikel, also die Grenzschicht zwischen Emissionsprodukt und Umwelt, als wirksamer Bereich interessiert, wurde eine oberflachenempfindliche Methode aus der Festkorperphysik, die Rontgen-Photoelektronenspektroskopie (XPS oder ESCA), erstmals in der Umweltanalytik eingesetzt. In diesem Beitrag werden vor allem die Mes- und Interpretationsmoglichkeiten behandelt. An eine Beschreibung der Versuchsbedingungen schliest sich eine Diskussion der Ergebnisse zweier Mesreihen an Diesel- und Ottomotoren, die in ihren Abgaswegen mit Rusfiltern bzw. Dreiwegekatalysatoren ausgerustet waren, an. Der Beitrag mochte auch dazu anregen, XPS verstarkt in der Umweltanalytik einzusetzen.