Hexagonally ordered arrays of non‐close‐packed nanoscaled spherical polystyrene (PS) particles are prepared exhibiting precisely controlled diameters and interparticle distances. For this purpose, a newly developed isotropic plasma etching process is applied to extended monolayers of PS colloids (starting diameters <300 nm) deposited onto hydrophilic silicon. Accurate size, shape, and smoothness control of such particles is accomplished by etching at low temperatures (−150 °C) with small rates not usually available in standard reactive ion etching equipment. The applicability of such PS arrays as masks for subsequent pattern transfer is demonstrated by fabricating arrays of cylindrical nanopores into Si.

Since the first proposal [1] by Aviram and Ratner to use organic molecules as new building blocks for information technology, tremendous efforts have been spent to implement basic electronic units such as rectifiers or transistors.[2] To fabricate appropriate metal-molecule-metal hybrid structures, two strategies have been followed in recent years, resulting in either planar or sandwich arrangements of the involved materials.[3] In the planar design, nanolithography at its current technological limits is required to manufacture metal electrodes with gaps precisely corresponding to the length of the molecules involved (1-3 nm). In the sandwich design, counter electrodes need to be deposited on top of molecular layers without destroying the assembly by interdiffusion. [3,4] The successful metallization of self-assembled organic monolayers (SAMs) can reliably be achieved with only a few methods.[3] Among those, electrochemical techniques [5,6] proved to be quite powerful, as they allow variation of both the type of molecules and the metals involved. [5][6][7][8][9] To increase the functionality of molecule-based nanoelectronic devices in the future, a significant increase in the complexity of their architecture might be required. As a vision, combinations of different molecular layers which can be electrically contacted by individual metal electrodes could serve as a new platform for this ambitious aim. Thus, it appears rather appealing to extend the sandwich design (one organic layer involved) to a molecular double decker (two separate organic layers) and, finally, to a molecular multilayer. Herein, we present theoretical and experimental evidence that a stable molecular double decker can be prepared, representing a proof-of-principle for the first step towards a 3D metal-molecule hybrid structure. The sample consists of a Au(111) single crystal as base electrode, a layer of 4-mercaptopyridine (Mpy) molecules forming the first SAM, a nearly closed Pd monolayer as a spacer, and a second Mpy SAM, which is metallized by a (sub-)monolayer of Pt atoms as the terminal electrode. We demonstrate that the Pd interlayer still reveals metallic properties despite the presence of two SAMs attached to it by chemical bonds. Such metallic interlayers might be useful as "intermediate electrodes" in future experiments, thus offering a new possibility to influence and control charge transport through metal-molecule hybrid structures.

Plasma etching of densely packed arrays of polystyrene particles leads to arrays of spherical nanostructures with adjustable diameters while keeping the periodicity fixed. A linear dependence between diameter of the particles and etching time was observed for particles down to sizes of sub-50 nm. Subsequent deposition of Co/Pt multilayers with perpendicular magnetic anisotropy onto these patterns leads to an exchange-decoupled, single-domain magnetic nanostructure array surrounded by a continuous magnetic film. The magnetic reversal characteristic of the film-particle system is dominated by domain nucleation and domain wall pinning at the particle locations, creating a percolated perpendicular media system.

ABSTRACT:A capacitive field-effect electrolyte-insulator-semiconductor (EIS) device was applied for the first time to trace the charge of supported gold nanoparticles (Au-NPs) induced by oxygen plasma treatment or due to storing in aqueous oxidation and reduction solutions. In addition, X-ray photoelectron spectroscopy (XPS) has been used as a reference method to establish the various charge states of the Au-NPs resulting from the different treatment steps. After the oxygen-plasma treatment, a shift of the capacitancevoltage (C-V) curve (and flatband potential) of the Au-NP-covered p-Si-SiO 2 EIS structure by about -300 mV was found. The exposure of the EIS sensor surface to an oxidative and a reductive solution resulted in a shift of the C-V curve for -85 and þ81 mV, respectively. These observations correlate well with corresponding binding energy shifts in Au 4f core spectra in XPS experiments. The obtained results may open new opportunities for biosensing and biochips based on nanoparticle-charge-gated field-effect devices.

Results from electrochemical studies, in situ STM, and ex situ angle-resolved XPS on self-assembled monolayers (SAMs) of thiazole on Au(111) are reported for the first time. Although STM seems to indicate a low density of molecules organized in small ordered domains, a quantitative chemical analysis of the sample surface by XPS clearly points toward the formation of a densely packed molecular layer. The stability of the thiazole SAM against reductive desorption is found to be very comparable with that for thiol-SAMs on gold. This results from the formation of Au-S bonds between the molecules and their support as evidenced by XPS, thereby rebuting speculations that the ring nitrogen is responsible for the attachment of such molecules to gold surfaces. Consequently, the N-atoms terminating the molecular layer are available as active sites for the complexation with Pd ions thereby allowing the deposition of Pd islands with monatomic height on top of the thiazole SAM. The importance of such studies for metal-molecule interconnections is briefly addressed.

Interactions between ethanol-water mixtures and a hydrophobic hydrogen terminated nanocrystalline diamond surface, are investigated by sessile drop contact angle measurements. The surface free energy of the hydrophobic surface, obtained with pure liquids, differs strongly from values obtained by ethanol-water mixtures. Here, a model which explains this difference is presented. The model suggests that, due to a higher affinity of ethanol for the hydrophobic surface, when compared to water, a phase separation occurs when a mixture of both liquids is in contact with the H-terminated diamond surface. These results are supported by a computational study giving insight in the affinity and related interaction at the liquid-solid interface.

Self-assembled monolayers of 1,4-dicyanobenzene on Au(111) electrodes are studied by cyclic voltammetry, in-situ STM and ex-situ XPS. High-resolution STM images reveal a long-range order of propeller-like assemblies each of which consists of three molecules, all lying flat on the gold substrate with the cyano groups oriented parallel to the metal surface. It is demonstrated that both functional groups can act as complexation sites for metal ions from solution. Surprisingly, such arrangements still allow the metal to be deposited on top of the molecules by electrochemical reduction despite the close vicinity to the Au surface. The latter is demonstrated by angle-resolved XPS which unequivocally shows that the metal indeed resides on top of the organic layer rather than underneath, despite the flat arrangement of the molecules.

A better understanding of the interactions between metal electrodes and organic molecules still represents one of the key problems in molecular electronics that needs be solved in order to optimize electron transport through a molecular device. In this contribution, the impact of widely used "alligator clips" (Au−thiol, Pd−pyridine) onto the electronic structure of the respective electrodes in metal− molecule−metal junctions has been studied using photoelectron spectroscopic tools. Different electronic properties are observed for molecules with different lengths but identical terminal groups, thereby elucidating a new aspect in the complex behavior of metal/molecule contacts.