occurring at ca. +1.20 V versus FeCp +/0 2 as well as reductions at potentials similar to those in our study (see (a) below). The HOMO level for perylene diimides can then be estimated as ca. 6.3 eV using E 1/2 (TPD +/0 ) -E 1/2 (PDI +/0 ) = E HOMO (TPD) -E HOMO (PDI),with E 1/2 (TPD +/0 ) = +0.26 V versus FeCp +/0 2 in CH 2 Cl 2 (see (b) below) and a value of 5.4 eV (from UV-PES; see (c) below) for E HOMO (TPD (s) Preparation and manipulation of supramolecular objects with nanometer dimensions in several of the three spatial directions are prominent goals of modern nanotechnology. [1] To date, nanosized objects, such as nanospheres, [2] nanowires, [3] or nanobelts [4] have been prepared from various materials, such as metals, ceramics, or organic polymers. Carbon nanotubes are another well-known example of supramolecular objects with one mesoscopically extended dimension and two others confined to the nanometer length scale.[5] Two-dimensionally extended nanomaterials have been prepared, e.g., from polyelectrolyte multilayers, with a thickness between 10 and 15 nm.[6] Similar freestanding polymeric membranes with thicknesses in the range of several tens of nanometers capable of spanning micrometerwide pores have been prepared from Langmuir-Blodgett monolayers of crosslinked polyisoprene, [7] from triblock copolymers, [8] and most recently from nanocomposite membranes of polyelectrolytes with embedded gold nanoparticles.[9] Extremely flat and two-dimensionally extended objects have been termed "nanosheets" and prepared, for example, by exfoliation of layered inorganic materials, with a thickness down to 1 nm and lateral dimensions up to 100 lm. [10,11] In this communication, we show the controlled preparation of individual, freestanding nanosheets with the thickness of a single biphenyl molecule. These nanosheets can span holes in the size range of several tens of micrometers. They can be prepared by electron-induced crosslinking of self-assembled monolayers and subsequent release of the material from its substrate. Self-assembled monolayers (SAMs) are highly ordered organic molecular aggregates chemisorbed on a surface with a thickness of a single molecule, i.e., in the range of a few nanometers. [12][13][14] SAMs containing aromatic bi-or terphenyl units can be laterally crosslinked by electron irradiation and are effective resist materials for nanopatterning. [15][16][17][18] During electron irradiation, carbon-hydrogen bonds are cleaved initially, followed by formation of carbon-carbon crosslinks between the aromatic units. Near-edge X-ray absorption fine structure spectroscopy (NEXAFS) [15,19,20] and infrared reflection absorption spectroscopy (IRRAS) [16] both indicate lower molecular order and reduced aromaticity of the crosslinked films.Other examples of crosslinked monolayers that have been previously reported include polymeric SAMs containing polydiacetylene units [21] and polymerized Langmuir-Blodgett films.[22] SAMs containing only aliphatic chains, such as alkanethiols on gold, are not crosslinked ...

Low-energy electron-induced damage in hexadecanethiolate (HDT) monolayers on gold substrates has been investigated using infrared reflection−absorption spectroscopy (IRAS), angle-resolved near edge X-ray absorption fine structure spectroscopy (NEXAFS), and advancing water contact angle measurements. HDT films were exposed to electrons of energies 10−100 eV and doses between 30 and 14 000 μC/cm2. The induced damage was monitored both “in situ” by NEXAFS measurements interleaved with electron irradiations and “ex-situ” by NEXAFS, IRAS, and contact angle measurements after exposure of the irradiated samples to air. A progressive film damage was observed with increasing electron energy and dose of irradiation. This damage was found to occur during irradiation in UHV and was not induced by chemical reactions with airborne molecules during subsequent exposure of the irradiated films to air. The damage starts in the region of the terminal methyl groups of the HDT films and propagates into the bulk of the film. An analysis of the IRAS and NEXAFS data shows that the conformational and orientational order within the HDT film are most sensitive to low-energy electron irradiation. Electron-induced cleavage of C−H and C−C bonds resulting in a partial desorption of the film constituents also occurs and leads to formation of CC double bonds in the film as inferred from the appearance of a π*-resonance in the C 1s NEXAFS spectra. The obtained results are of importance for both the optimization of self-assembled-monolayers-based lithography processes and for the general understanding of irradiation-induced changes in organic films.

In this article we describe the preparation and identification of an organosilane self-assembled monolayer (octadecyltrimethoxysilane:  OTMS) on chromium oxide. The formation of the OTMS monolayer was investigated by X-ray photoelectron (XPS) spectroscopy and water contact angle measurements. Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy was applied in order to determine the tilt angle of the alkyl chains in the monolayer. The degree of hydration of the chromium oxide surface was found to greatly influence the quality of the monolayer. Our work focuses on the suitability of OTMS/Cr for lithographic patterning with low-energy electrons. In addition to the sensitivity and selectivity of the SAM system, its contrast γ was determined by measuring the gradation curve of OTMS on a 20 nm thick chromium layer using an alkaline hexacyanoferrat solution as an etchant. The contrast was found to be γ ≈ 1, which is comparable to those of conventional electron resists. The structured chromium layer was used as a mask for a reactive ion etch (RIE) process to pattern a silicon substrate.

A low energy electron point source microscope is used to determine the electrical conductivity of freestanding ZnO nanowires. The nanowires were contacted with a manipulation tip and I-V curves were taken at different wire lengths. From those, the specific resistance was calculated and separated from the contact resistance. By comparing the specific resistances of ZnO nanowires with diameters between 1100 and 48nm, a large surface contribution for the thin nanowires was found. A geometric model for separation between surface and bulk contributions is given.