Nicole Herzer

Fabrication of patterned silane based self-assembled monolayers by photolithography and surface reactions on silicon-oxide substrates

Self-assembled monolayers (SAMs) have received increasing attention since their introduction 30 years ago. Soon it was discovered that they can be used as alternative resist materials and are compatible with different established lithographic techniques commonly used in silicon semiconductor technology. Besides these possibilities to structure SAMs, other attractive properties emerged from the use of SAMs. E.g., the introduction of addressability into the patterns by selective functionalization with reactive precursor molecules and/or by applying suitable surface reactions was established. In this feature we highlight developments of photolithographic techniques that have been used in combination with SAMs serving either as resists for the patterning process or as precursor molecules for surface reactions, which can be performed on non-structured and mainly photochemically structured surfaces to obtain multifunctional surfaces with tunable surface properties. The aim is to provide an overview about the versatile possibilities to use silane based SAM systems to structure silicon-oxide substrates by introducing topographical as well as chemically heterogeneous surface structures. In particular the chemical activation of SAMs includes a large number of functionalization concepts which are intended to be summarized in this review. They will be introduced here according to the class of chemical reaction that has been used. Therefore, an introduction into the plethora of possible structures, which have been created by the combination of photolithographic structuring approaches, and the integration of tailor made surface functionalities into these systems will be highlighted. Additionally effective strategies to implement a diversity of chemical functionalities onto one substrate are summarized.

Printable Optical Sensors Based on H-Bonded Supramolecular Cholesteric Liquid Crystal Networks

A printable H-bonded cholesteric liquid crystal (CLC) polymer film has been fabricated that, after conversion to a hygroscopic polymer salt film, responds to temperature and humidity by changing its reflection color. Fast-responding humidity sensors have been made in which the reflection color changes between green and yellow depending on the relative humidity. The change in reflection band is a result of a change in helix pitch in the film due to absorption and desorption of water, resulting in swelling/deswelling of the film material. When the polymer salt was saturated with water, a red-reflecting film was obtained that can potentially act as a time/temperature integrator. Finally, the films were printed on a foil, showing the potential application of supramolecular CLC materials as low-cost, printable, battery-free optical sensors.

Orthogonal functionalization of silicon substrates using self-assembled monolayers.

A fabrication process for multifunctional surfaces is designed leading to five different functional moieties (amine, thiol, carboxylic acid, fluoro, and methyl) being present on a single structured surface. The multifunctional surface is created by combining UV-ozone patterning, electro-oxidative lithography, the local deposition of self-assembled monolayers (SAMs), and surface modification schemes. Besides the characterization with conventional surface-sensitive techniques, the nature of the locally functionalized regions is demonstrated by self-assembly of three different probe nanomaterials (Si nanoparticles, Au nanoparticles, and hydroxyl functionalized micelles). A versatile fabrication approach for complex surfaces with addressable functionalities can be created, and it was possible to integrate five different functionalized areas on one substrate.

Unexpected metal-mediated oxidation of hydroxymethyl groups to coordinated carboxylate groups by bis-cyclometalated iridium(III) centers

Two different procedures of the ‘click’ reaction were applied to synthesize a library of 1-aryl- and 4-aryl-functionalized 1H-[1,2,3]triazoles as new ligands for phosphorescent iridium(III) complexes. For three examples, single crystal X-ray analysis was carried out and the structural properties were discussed. The reactive μ-dihydroxy-bridged iridium(III) precursor complex [(ppy)2Ir-μ-(OH)]2 (ppy = 2-phenylpyridinato) was prepared for the complexation of the herein described ligands. During these complexation studies, an unexpected metal-assisted oxidation pathway was observed for the hydroxymethyl-substituted 1-aryl-1H-[1,2,3]triazoles 2d–f leading selectively to a [carboxylate-N3,O]-coordination of the ligands to the iridium(III) centers.

Fabrication of PEDOT–OTS-patterned ITO substrates

The fabrication of a poly(3,4-ethylenedioxythiophene) (PEDOT) pattern is demonstrated. As template, an n-octadecyltrichlorosilane (OTS) monolayer self-assembled on indium tin oxide (ITO) was structured by UV–ozone photolithography, resulting in an ITO–OTS patterned surface. The conducting properties of the ITO were utilized for the selective electropolymerization of 3,4-ethylenedioxythiophene (EDOT), whereby the electropolymerization was inhibited by the insulating OTS. Differently sized PEDOT–OTS patterns were obtained. The electronic properties of the patterns were finally evaluated in a test OLED device.

Fabrication of ring structures by anodization lithography on self-assembled OTS monolayers

A new and rational fabrication concept to obtain ring structures with nanometer dimensions is presented that utilizes a combination of anodization and electrochemical oxidation lithography on a self-assembled monolayer of n-octadecyltrichlorosilane performed with an electrically biased scanning force microscopy tip. During the oxidation process two different chemical areas are created; a silicon oxide core which is surrounded by a chemically active, acid functionalized rim feature. The oxidation conditions, as well as the scaling options of this lithographic process have been investigated and revealed good controllability of the ring dimensions. A straightforward electroless metal deposition process was used to convert the ring structures into metal features.