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Matthias Geissler

Publications and source records attributed to Matthias Geissler.

7 recordsLinked to original sources
PubMed2005

Edge-spreading lithography: use of patterned photoresist structures to direct the spreading of alkanethiols on gold.

Edge-spreading lithography (ESL) has been extended to fabricate gold structures with different geometries and feature sizes on silicon substrates. In the present variant of ESL, we used photoresist structures patterned on a thin film of gold to transport alkanethiol molecules from an elastomeric stamp to the gold surface where they formed a self-assembled monolayer (SAM) along the edge of each resist feature. The emerging SAM could expand laterally on the gold via reactive spreading, during which the footprints of the resist structures were enlarged in the same fashion. Upon removal of the photoresist, selective etching of gold revealed those regions that were protected by the SAM, yielding accurate outlines of the resist features on the substrate. The width of resultant gold structures was determined by the distance over which the monolayer expanded during spreading, and could be conveniently controlled well below 200 nm by varying the contact time and/or the concentration of alkanethiol in the ink.

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PubMed2004

Single-crystal nanowires of platinum can be synthesized by controlling the reaction rate of a polyol process.

Platinum nanowires of approximately 100 nm in length and approximately 5 nm in diameter have been synthesized by reducing H(2)PtCl(6) with ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP) and a trace amount of Fe(3+) or Fe(2+). The wires were generated at the final stage of the synthesis, which involved the formation of several intermediate species. The Fe(3+) or Fe(2+) ions had dual functions in the synthesis: they induced aggregation of Pt nanoparticles into larger structures that served as the nucleation sites, and they greatly reduced the reaction rate and supersaturation level to induce anisotropic growth. The reaction mechanism was studied by X-ray photoelectron spectroscopy (XPS) and UV-vis spectral analysis. The Pt nanowires could be readily separated from the surfaces of the agglomerates by sonication and obtained as pure samples by centrifugation.

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PubMed2004

Edge spreading lithography and its application to the fabrication of mesoscopic gold and silver rings.

A new form of edge lithography, edge spreading lithography (ESL), has been demonstrated and applied to the formation of coinage metal rings. In this process, alkanethiols are delivered from a flat PDMS stamp to the surface of a metal film through a two-dimensional array of spherical silica colloids. The thiols further spread on the metal surface, forming highly ordered SAMs in the form of a ring pattern. Following lift-off of beads, the pattern in the SAMs can be transferred into the metal film through wet chemical etching, with SAMs serving as the resist. The dimensions of the rings can be readily controlled by several parameters such as the beads diameter, the concentration of the thiol solution, and the contact time between the stamp and the silica beads.

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PubMed2004

Comparative study of monolayers self-assembled from alkylisocyanides and alkanethiols on polycrystalline Pt substrates.

This paper compares the properties of self-assembled monolayers (SAMs) derived from octadecylisocyanide (ODI) and octadecanethiol (ODT) on polycrystalline Pt substrates. Both monolayers formed at a similar rate using 1.0 mM solutions in ethanol and achieved a thickness of 22-23 A after 24 h as determined by ellipsometry measurements. The advancing contact angles of ODI and ODT monolayers were found to be 113 and 117 degrees, respectively, suggesting a slight difference in structure between them. X-ray photoelectron spectroscopy revealed that SAMs of ODT were more stable than those of ODI, which was supported by experiments that probed desorption of these layers in prewarmed hexadecane. Cyclic voltammetry measurements indicated that both monolayer systems could diminish electron-transfer rates substantially, although ODT monolayers were more effective and robust than their ODI counterparts. The resistance of the SAMs to ion penetration differed in a similar way, and a microcontact-printed monolayer of ODT could protect the underlying Pt better in an HCl/Cl2-based etch process than the one formed from ODI.

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PubMed2002

Positive microcontact printing.

Microcontact printing alkanethiols from an inked, microstructured stamp onto Au or Cu results in the formation of a self-assembled monolayer, which can locally protect the substrate from wet etching. This lithographic technique resembles a negative-type of lithography but can be inverted to the positive process. This is done by printing a type of oligothiol that does not protect the substrate from etching but prevents the adsorption of a protective monolayer from solution.

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