Gold nanoparticles ranging in diameter from 1 to 8 nanometers were prepared on top of silicon wafers in order to study the size dependence of their oxidation behavior when exposed to atomic oxygen. X-ray photoelectron spectroscopy showed a maximum oxidation resistance for "magic-number" clusters containing 55 gold atoms. This inertness is not related to electron confinement leading to a size-induced metal-to-insulator transition, but rather seems to be linked to the closed-shell structure of such magic clusters. The result additionally suggests that gold-55 clusters may act as especially effective oxidation catalysts, such as for oxidizing carbon monoxide.

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.

Gold nanoclusters of a size approaching the molecular limit (<3 nm) were prepared on Si substrates in order to study alloy formation on the nanometer scale. For this purpose, indium atoms are deposited on top of the gold particles at room temperature and the formation of AuIn(2) is studied by x-ray photoelectron spectroscopy in situ. It is observed that the alloy formation takes place independent of whether the particles electronically are in an insulating molecular or in a metallic state. Most important, however, closed packed full-shell clusters containing 55 Au atoms are found to exhibit an outstanding stability against alloying despite a large negative heat of formation of the bulk Au-In system. Thus, Au(55) clusters may play a significant role in the design of nanoscaled devices where chemical inertness is of crucial importance.

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...

Starting with Co‐salt‐loaded inverse micelles, which form if the diblock copolymer polystyrene‐block‐poly(2‐vinylpyridine) is dissolved in a selective solvent like toluene and CoCl2 is added to the solution, monomicellar arrays of such micelles exhibiting a significant hexagonal order can be prepared on top of various substrates with tailored intermicellar distances and structure heights. In order to remove the polymer matrix and to finally obtain arrays of pure Co nanoparticles, the micelles are first exposed to an oxygen plasma, followed by a treatment in a hydrogen plasma. Applying in‐situ X‐ray photoelectron spectroscopy, it is demonstrated that: 1) The oxygen plasma completely removes the polymer, though conserving the original order of the micellar array. Furthermore, the resulting nanoparticles are entirely oxidized with a chemical shift of the Co 2p3/2 line pointing to the formation of Co3O4. 2) By the subsequent hydrogen plasma treatment the nanoparticles are fully reduced to metallic Co. 3) By exposing the pure Co nanoparticles for 100 s to various oxygen partial pressures p, a stepwise oxidation is observed with a still metallic Co core surrounded by an oxide shell. The data allow the extraction of the thickness of the oxide shell as a function of the total exposure to oxygen (p × time), thus giving the opportunity to control the ferromagnetic–antiferromagnetic composition of an exchange‐biased magnetic system.