Andreas Aumann

Using Laser Microfabrication to Write Conductive Polymer/SWNTs Nanocomposites

We present a novel laser microfabrication method to generate structures on the basis of a new class of functional photosensitive composites. particular, the focus lies Inon the development of conductive composites by incorporatingSWNTs into the matrix of polymers thus forming highly conductive nanocomposites. Conductive microstructures have been produced with the ultra-high resolution technology based on laser direct writing (e.g. single-, two-photon polymerization) using polymer/SWNTs nanocomposites. This technology opens new prospects for the realization of novel MEMS and MOEMS with increased functionality, integration, and higher level of miniaturization.

Micro-patterning of self-assembled organic monolayers by using tunable ultrafast laser pulses

We study the application of tunable ultrafast laser pulses in micropatterning self- assembled organic monolayer (SAMs) employing non collinear optical parametric amplification (NOPA). SAMs are ultrathin organic monolayers, which can be used in a variety of ways to assemble functionalized surface structures. In our study, we investigate the characteristics of SAMs as monomolecular resists during etching of gold. NOPA is a versatile method which provides the generation of ultrafast laser pulses, with a tunable wavelength in the visible and near infrared range. Due to the noncollinear geometry, a broadened spectral range can be amplified. The NOPA delivers wavelengths in the range of 480 nm to 950 nm at laser pulse lengths in the sub- 30 femtosecond range using a prism compressor after the nonlinear conversion. The ultrashort laser technology together with the advantages of the NOPA system guarantee high precision and allows us to determine the optimum conditions of sub-wavelength patterning by studying the effects of the fluence and the wavelength. At the same time, single-pulse processing allows us to selectively remove the ultrathin organic coating, while it ensures short processing time. In our study we used thiol-based SAMs as ultrathin layers on gold-coated glass substrates with a film thickness of 1-2 nm and 40 nm respectively.

Holographic optical tweezers: microassembling of shape-complementary 2PP building blocks

Based on an ongoing trend in miniaturization and due to the increased complexity in MEMS-technology new methods of assembly need to be developed. Recent developments show that particularly optical forces are suitable to meet the requirements. The unique advantages of optical tweezers (OT) are attractive due to their contactless and precise manipulation forces. Spherical as well as non-spherical shaped pre-forms can already be assembled arbitrarily by using appropriate beam profiles generated by a spatial light modulator (SLM), resulting in a so called holographic optical tweezer (HOT) setup. For the fabrication of shape-complementary pre-forms, a two-photon-polymerization (2PP) process is implemented. The purpose of the process combination of 2PP and HOT is the development of an optical microprocessing platform for assembling arbitrary building blocks. Here, the optimization of the 2PP and HOT processes is described in order to allow the fabrication and 3D assembling of interlocking components. Results include the analysis of the dependence of low and high qualities of 2PP microstructures and their manufacturing accuracy for further HOT assembling processes. Besides, the applied detachable interlocking connections of the 2PP building blocks are visualized by an application example. In the long-term a full optical assembly method without applying any mechanical forces can thus be realized.

Ex-situ preparation of high-conductive polymer/SWNTs nanocomposites for structure fabrication

This paper reports ex-situ preparation of conductive polymer/single-walled carbon nanotubes (SWNTs) nanocomposites by adding high conductive SWNTs to the polymer matrix. Sonication methods were used to disperse the SWNTs in the polymer. The conductivity of the nanocomposites is tuned by increasing the concentration of SWNTs. Furthermore, we present two-photon polymerization (2PP) method to fabricate structures on the basis of conductive photosensitive composites. The conductive structures were successfully generated by means of 2PP effect induced by a femtosecond laser.

Resolution and aspect ratio in two-photon lithography of positive photoresist

In this work, the authors report on investigations of two-photon lithography of positive photoresist. The dependency of the pattern linewidth on variation in the processing parameters, like the laser patterning velocity or power of the femtosecond laser oscillator, is presented. The influence of the scan velocity between 0.38 and 1.90 mm/s on the resolution is discussed for a layer thickness of 3.5 μm. By using a commercial positive photoresist, an aspect ratio of 5 has been realized for grid structures and the qualities of the produced structures are discussed.

Optical micro-assembling of non-spherical particles

Holographic optical tweezers have been developed for the manipulation of polymeric microparticles or biological cells with almost circular shape. As is well known, spherical particles can be trapped and controlled by optical tweezers and assembled with an additional light modulator application. Complementary building blocks, which are used in the following experiments, are generated by a two-photon-polymerization process in micrometer range and are not equipped with spherical trapping points. The possibilities of manufacturing arbitrary building blocks within the 2PP process and the potential of HOTs lead to the idea of combining manufacturing techniques with manipulation processes in a bottomup operation. In this work we present an experimental setup with an integrated fiber laser for holographic optical trapping of non-spherical building blocks. Furthermore experimental requirements which permit trapping will be illustrated.

A modular assembling platform for manufacturing of microsystems by optical tweezers

Due to the increased complexity in terms of materials and geometries for microsystems new assembling techniques are required. Assembling techniques from the semiconductor industry are often very specific and cannot fulfill all specifications in more complex microsystems. Therefore, holographic optical tweezers are applied to manipulate structures in micrometer range with highest flexibility and precision. As is well known non-spherical assemblies can be trapped and controlled by laser light and assembled with an additional light modulator application, where the incident laser beam is rearranged into flexible light patterns in order to generate multiple spots. The complementary building blocks are generated by a two-photon-polymerization process. The possibilities of manufacturing arbitrary microstructures and the potential of optical tweezers lead to the idea of combining manufacturing techniques with manipulation processes to “microrobotic” processes. This work presents the manipulation of generated complex microstructures with optical tools as well as a storage solution for 2PP assemblies. A sample holder has been developed for the manual feeding of 2PP building blocks. Furthermore, a modular assembling platform has been constructed for an ‘all-in-one’ 2PP manufacturing process as a dedicated storage system. The long-term objective is the automation process of feeding and storage of several different 2PP micro-assemblies to realize an automated assembly process.

Sub-wavelength patterning of self-assembled organic monolayers via non-collinear optical parametric amplifier

Self-assembled monolayers (SAMs) are ultra-thin organic monolayers, which can be used in different ways to assemble functionalized surface structures. This potential is caused by the ability of the SAMs to tie further molecules and components through the terminal groups of the organic layers. Additional applications for microfluidics and micromechanics require micro and nano structuring of the SAMs. In combination with multi-photon lithography (MPL) SAMs are offering advantageous properties as ultra thin layers. Thus, the processing with single pulses is feasible and results in very short processing times without the appearance of bubbles and formation of particles compared to photo resists. For our experiments, we used a non-collinear optical parametric amplifier (NOPA) which has the ability to generate short pulses of sub-30fs in the visible and near-infrared (NIR) range of light. The NOPA can be tuned in the range of 480 nm to 950 nm without spectral gaps.We used thiol based SAMs as ultra thin layers on gold substrates. The selected laser power offers the possibility of ablation of the SAMs without damaging the gold layer. Thereby we investigate the characteristics of thiol-based SAMs as monomolecular resists during etching of gold. We also investigate the wavelength dependencies of the substrate to get an optimal process window for the ablation process. Minimum structure sizes at a 1/e laser spot diameter of about 1.6 µm are close to 1/5 of the spot diameter.Self-assembled monolayers (SAMs) are ultra-thin organic monolayers, which can be used in different ways to assemble functionalized surface structures. This potential is caused by the ability of the SAMs to tie further molecules and components through the terminal groups of the organic layers. Additional applications for microfluidics and micromechanics require micro and nano structuring of the SAMs. In combination with multi-photon lithography (MPL) SAMs are offering advantageous properties as ultra thin layers. Thus, the processing with single pulses is feasible and results in very short processing times without the appearance of bubbles and formation of particles compared to photo resists. For our experiments, we used a non-collinear optical parametric amplifier (NOPA) which has the ability to generate short pulses of sub-30fs in the visible and near-infrared (NIR) range of light. The NOPA can be tuned in the range of 480 nm to 950 nm without spectral gaps.We used thiol based SAMs as ultra thin layers o...