Clarifying the nature of interactions between metal electrodes and organic molecules still represent one of the challenging problems in molecular electronics that needs to be solved in order to optimize electron transport through a molecular device. For this purpose, electronic properties at metal-molecule interfaces were studied by combining experimental and theoretical methods. Applying a novel electrochemical approach, strictly two-dimensional Pd islands were prepared on top of 4-mercaptopyridine self-assembled monolayers (4MP-SAMs) which, in turn, were deposited on (111)-oriented Au single crystals. Electron spectroscopy together with density functional theory calculations revealed strong interactions between the molecules and the islands due to Pd-N bonds, resulting in a drastically reduced density of states (DOS) at the Fermi level EF for a nearly closed Pd monolayer, and even non-metallic properties for nanometre-sized islands. Similarly, a significantly reduced DOS at EF was observed for the topmost Au layer at the Au-SAM interface due to Au-S interactions, suggesting that these effects are rather general.

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) L1 0 FePt alloy belongs to the promising class of materials that offer the perspective of storing one magnetic bit per nanoparticle. [1][2][3] Widespread activities have therefore arisen worldwide, targeting novel strategies for both the synthesis [1,[4][5][6][7][8][9][10][11][12][13][14] of suitable magnetic nanostructures and their organization into superlattices [4,12,[15][16][17][18] by means of parallel processes. Here, we present a new approach for the synthesis of size-selected L1 0 FePt nanoparticles based on the self-organization of spherical micelles formed by diblock copolymers, thereby significantly extending a previous technique [19][20][21] 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 -2 (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 -2 , as found in present hard disk drives.[22]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.[1] 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. [23,24] 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 L1 0 phase. Furthermore, undesirable collective magnetic dynamics arise at such small interparticle distances through dipolar coupling; [24,25] 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.[26]Recent alternative routes for the synthesis of L1 0 FePt nanoparticles include...

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Small organic molecules as potential building-blocks for future nanoelectronic devices [1][2][3][4][5] 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 [6] that allows detection of small aromatic units like 4-aminothiophenol (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 the metal electrodes in such a molecular junction.For this purpose, a 4-ATP self-assembled monolayer (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. [7][8][9][10] 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.[11] 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 À0.1 V vs. standard calomel electrode (SCE), which may be considered an appropriate means for desolving any thiol in excess of the first layer.[12] In Figure 1 cyclic voltammograms are shown for Au(111) in 0.1 M H 2 SO 4 , after the electrode had been immersed for 15 min in a 0.1 Â 10 À3 M 4-ATP/0.1 M H 2 SO 4 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)...